Fix ``mypy`` Errors

[SterlingPeet]

🛰️ Overview

Fix mypy typing errors in the codebase. There are no functional adjustments being made to the code.

✨ Change Description/Rationale

• 🚨 Fix no_implicit_optional type hinting error

PEP 484 prohibits implicit Optional. Accordingly, mypy has changed its default to no_implicit_optional=True

The tool https://github.com/hauntsaninja/no_implicit_optional was used to automatically upgrade the codebase.

• 🚨 Fix incompatible types assignment in main function signature

The following error in mypy is a result of re-assigning arguments:

error: Incompatible types in assignment (expression has type "Namespace", variable has type "Optional[List[str]]") [assignment]

The solution is to avoid the use of the pattern that argparse suggests, because it causes type shadowing that is hard for humans and hard for mypy to read. The following resource does a good job explaining the problem and solution:

https://adamj.eu/tech/2021/05/23/python-type-hints-mypy-doesnt-allow-variables-to-change-type/

🧪 Test Coverage

There are no changes relevant to this section.

🚨 Quality Deviations

Test do not pass, but that will be handled in a different PR.

👀 Reviewer Checklist

• [x] Run tox -e mypy to see that the code is now type-hinted correctly.

✅ PR Checklist

• [x] Remove or update the PR template boilerplate text
• [x] Reviewers Requested
• [x] Labels added
• [x] Projects associated
• [x] Milestone assigned
• [x] All docstrings are formatted as google docstrings with filled out types and explanations; Any code that was edited and contains a prose description of the functional execution, and preferably a doctest compatible example
• [x] Docstring examples are all doctest compliant
• [x] Any file or folder names are manipulated via pathlib.Path
• [x] Non-public imports and API elements are prefixed with a single underscore or the package __all__ variable is set
• [x] All noqa statements for skipping lint rules are justified
• [x] Commits mention issue and/or PR numbers at the bottom of the message with the Username/Repository# format
• [x] Relevant issues are linked into the PR (issues mentioned in overview should link for you)
• [x] TODOs are completed
• [x] Reviewer checklist is updated

🚀 TODOs

• [x] None

📌 Future Work

• Tests do not pass and will be addressed in a future PR.

[SterlingPeet]

@LeStarch I have added you to this PR largely because it serves as an example of how PRs should look for this repo.