refactor: improve overall repo structure

.gitattributes

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+# Normalise line endings automatically for files detected as text by default.
+# That is: let the git installation on a user's machine decide
+# which line ending to use when a repository is checked out.
+# Subsequent lines may override this setting.
+*                                      text=auto
+
+# recognise file syntax during diff
+*.hpp                                  text diff=cpp
+*.cpp                                  text diff=cpp
+*.tex                                  text diff=tex
+*.bib                                  text diff=bibtex
+*.md                                   text diff=markdown
+*.sh                                   text diff=bash
+
+# force batch scripts to always use CRLF
+*.cmd                                  text eol=crlf
+*.bat                                  text eol=crlf
+
+# force bash scripts & Makefile to always use LF
+*.sh                                   text eol=lf
+Makefile                               text eol=lf
+
+# mark binary files explicitly
+# (Git does not try to merge these files)
+# binary is a built-in macro attribute == -diff -merge -text
+*.png                                  binary
+
+# specify which files/dirs to ignore on [download ZIP] (not a git repo)
+.github                                export-ignore
+.test                                  export-ignore
+.docs                                  export-ignore
+img                                    export-ignore
+.gitattributes                         export-ignore
+.gitignore                             export-ignore
+.gitpod.dockerfile                     export-ignore
+.gitpod.yml                            export-ignore
+.pre-commit-config.yaml                export-ignore
+CODE_OF_CONDUCT.md                     export-ignore
+codecov.yml                            export-ignore
+CODEOWNERS                             export-ignore
+CONTRIBUTING.md                        export-ignore
+Doxyfile                               export-ignore
+environment.yml                        export-ignore
+meta.yaml                              export-ignore
+paper.bib                              export-ignore
+paper.md                               export-ignore
+
+# linguist settings:
+#
+# Gitpod configuration files
+.gitpod.dockerfile                     -linguist-detectable
+.gitpod.yml                            -linguist-detectable
+# Dev Docker/env
+Dockerfile                             -linguist-detectable
+entrypoint.sh                          -linguist-detectable
+environment.yml                        -linguist-detectable
+# Catch2 test framework
+.test/unit/catch.hpp                   -linguist-detectable

.github/ISSUE_TEMPLATE/BLANK_TEMPLATE.yml

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+---
+name: "Blank Template 💬"
+about: Empty template for special occasions only
+labels:
+---

.github/ISSUE_TEMPLATE/BUG_REPORT_TEMPLATE.yml

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+name: Bug Report 🐛
+description: Create a bug report
+title: "<descriptive title goes here>"
+labels: [bug]
+body:
+  - type: markdown
+    attributes:
+          value: |
+            Thank you for your interest in this project!
+
+            Please read the following instructions carefully.
+            Having detailed, yet not overcomplicated feedback will help us resolve the issue efficiently 🚀
+
+            **Before reporting a bug, please search for a similar problem in the issues section**
+  - type: checkboxes
+    id: checks
+    attributes:
+      label: Initial check.
+      description: Please go through the options carefully.
+      options:
+        - label: I added a very descriptive title above.
+          required: true
+        - label: I searched through the issues in this repository to find a similar problem, but didn't find any.
+          required: true
+        - label: I searched the documentation and found no explanation.
+          required: true
+        - label: I searched through Google (including the 2nd page of results) and didn't find any relevant information.
+          required: true
+        - label: I asked ChatGPT for help but did not get any meaningful response.
+          required: false
+  - type: textarea
+    id: description
+    attributes:
+      label: Please describe what triggered the error.
+      description: Add a self-contained, [minimal, reproducible, example](https://stackoverflow.com/help/minimal-reproducible-example) with your use case.
+      placeholder: If you can copy it, run it, and see it right away, there's a much higher chance someone will be able to help you.
+    validations:
+      required: true
+  - type: textarea
+    id: expected
+    attributes:
+      label: What did you expect to happen?
+      description: How should the program behave without the bug?
+      placeholder: Describe the ideal outcome.
+    validations:
+      required: true
+  - type: textarea
+    id: error
+    attributes:
+      label: What went wrong?
+      description: What kind of error message did you get?
+      placeholder: You should add terminal logs.
+    validations:
+      required: true
+  - type: input
+    id: gpp_version
+    attributes:
+      label: Please specify your compiler's version.
+      placeholder: g++ --version
+    validations:
+      required: true
+  - type: dropdown
+    id: os_version
+    attributes:
+      label: Operating System
+      options:
+        - Linux
+        - macOS
+        - Microsoft Windows
+        - Other
+    validations:
+      required: true
+  - type: checkboxes
+    id: terms
+    attributes:
+      label: Code of Conduct
+      options:
+        - label: I agree to follow this project's [Code of Conduct](https://github.com/AngryMaciek/hypercomplex/blob/master/CODE_OF_CONDUCT.md)
+          required: true
+  - type: textarea
+    id: context
+    attributes:
+      label: Additional information
+      description: Add any additional context or screenshots you think might be useful or helpful.
+    validations:
+      required: false
+  - type: markdown
+    attributes:
+      value: |
+
+
+        *Thank you for your contribution!*

.github/ISSUE_TEMPLATE/FEATURE_REQUEST_TEMPLATE.yml

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+name: Feature Request 💡
+description: Suggest an idea for improvement
+title: "<descriptive title goes here>"
+labels:
+  - enhancement
+body:
+  - type: markdown
+    attributes:
+          value: |
+            Thank you for your interest in this project!
+
+            Please read the following instructions carefully.
+            Having detailed, yet not overcomplicated feedback will help us implement the idea efficiently 🚀
+
+            **Before suggesting an idea, please search for a similar feature request in the issues section**
+  - type: checkboxes
+    id: checks
+    attributes:
+      label: Initial check.
+      description: Please go through the options carefully.
+      options:
+        - label: I added a very descriptive title above.
+          required: true
+        - label: I searched the documentation and found no similar feature.
+          required: true
+        - label:  I searched through the issues in this repository to find a similar request, but didn't find any.
+          required: true
+  - type: textarea
+    id: description
+    attributes:
+      label: Describe briefly the idea behind the improvement.
+      description: When would it be useful? What problem would it solve?
+      placeholder: Try to come up with a use case
+    validations:
+      required: true
+  - type: textarea
+    id: ideas
+    attributes:
+      label: Please specify what would you like to add/change.
+      description: How would you make your idea come true?
+      placeholder: You may inclue code snippets
+    validations:
+      required: true
+  - type: textarea
+    id: alternatives
+    attributes:
+      label: Please add other solutions if you considered them.
+      description: Alternative ways to bring your idea to life.
+      placeholder: First thought best thought?
+    validations:
+      required: false
+  - type: textarea
+    id: supplement
+    attributes:
+      label: Feel free to provide additional information or more context for your idea.
+      description: Screenshots or other information you find worth sharing; anything the developers might find useful.
+      placeholder:
+    validations:
+      required: false
+  - type: checkboxes
+    id: terms
+    attributes:
+      label: Code of Conduct
+      description: By submitting this feature request, you agree to follow our Code of Conduct.
+      options:
+        - label: I agree to follow this project's [Code of Conduct](https://github.com/AngryMaciek/hypercomplex/blob/master/CODE_OF_CONDUCT.md)
+          required: true
+  - type: markdown
+    attributes:
+      value: |
+        *Keep the ideas coming!*

.github/ISSUE_TEMPLATE/config.yml

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+blank_issues_enabled: false
+contact_links:
+  - name: Security or Code of Conduct violation
+    about: Please report security or behaviour issues to wsciekly.maciek@gmail.com

.github/PULL_REQUEST_TEMPLATE.md

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+## Proposed changes ⤴️
+
+Describe the big picture of your changes, add relevant motivation and context.
+
+**If it fixes a bug or resolves a feature request, please link a corresponding issue:**
+Fixes #
+
+## Types of changes 🔧
+
+What type of changes does your code introduce to the project?
+
+- [ ] Bugfix (non-breaking change which fixes an issue)
+- [ ] New feature (non-breaking change which adds functionality)
+- [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
+- [ ] Other
+
+## Checklist ✅
+
+If you're unsure about any of those below, ask explicitly.
+This is simply a reminder of what needs to be checked before merging your code.
+
+- [ ] I have read the [CONTRIBUTING](https://github.com/AngryMaciek/hypercomplex/blob/master/CONTRIBUTING.md).
+- [ ] I have performed a self-review of my own code.
+- [ ] Tests specified with the 'make' framework do not raise any errors.
+- [ ] I have added tests that prove my fix is effective or that my feature works.
+- [ ] I have added necessary documentation (if appropriate).
+- [ ] My changes generate no new warnings.
+- [ ] I have commented my code, particularly in hard-to-understand areas.
+
+## Further comments 🧠
+
+If this is a relatively large or complex change feel free to provide additional information or explanation.