Update mypy and fix issues

[bryanforbes]

Pull Request Check List

• Added tests for changed code.
• Updated documentation for changed code.

This upgrades mypy to 0.991 and fixes the errors associated with it. I've also removed the mypy check from pre-commit and added a type checking step during unit testing. This requires running poetry install twice to remove the type checking dependencies to ensure that there are no runtime dependencies on the type checking libraries (like typing_extensions). Another option would be to change the pre-commit config to use mypy via poetry, remove the third-party pre-commit PR hook, and add a Github action that invokes pre-commit with the proper poetry install. That can be done as a separate PR, though.

[codspeed-hq]

CodSpeed Performance Report

Merging #680 feature/mypy-improvement (681be2d) will not alter performances.

Summary

🔥 0 improvements
❌ 0 regressions
✅ 2 untouched benchmarks

🆕 0 new benchmarks
⁉️ 0 dropped benchmarks

[Secrus]

@bryanforbes could you update to the latest version of mypy and fix potential issues? I will have some time this weekend and want to merge this.

[bryanforbes]

@Secrus this is ready to go