feat: add reddit slash commands

[ReenigneArcher]

Description

• Add slash commands for reddit
• Remove last_online file
• shelve now handles comments and submissions
• Added function to migrate previous shelve
• Improve reddit unit testing

Screenshot

Issues Fixed or Closed

Type of Change

• Bug fix (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)
• Dependency update (updates to dependencies)
• Documentation update (changes to documentation)
• Repository update (changes to repository files, e.g. .github/...)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated the in code docstring/documentation-blocks for new or existing methods/components

Branch Updates

LizardByte requires that branches be up-to-date before merging. This means that after any PR is merged, this branch
must be updated before it can be merged. You must also
Allow edits from maintainers.

• I want maintainers to keep my branch updated

[codecov]

Codecov Report

Attention: Patch coverage is 89.70588% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 42.95%. Comparing base (ad71781) to head (5c98def).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #281      +/-   ##
==========================================
+ Coverage   37.86%   42.95%   +5.08%     
==========================================
  Files          15       15              
  Lines         853      873      +20     
==========================================
+ Hits          323      375      +52     
+ Misses        530      498      -32     

Files	Coverage Δ
src/reddit/bot.py	80.25% <89.70%> (+26.24%)	⬆️