Mypy checks + fixes

[MissingNO57]

• Additional linting checks (MyPy)

• removed
  repo_root_path = Path(__file__).parent.parent.parent.absolute() sys.path.insert(0, str(repo_root_path))

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Code Review Checklist (to be filled out by reviewer)

• Description accurately reflects what changes are being made.
• Either the PR references an issue (via the "Development" combobox) or the description explains the need for the changes.
• The PR appropriately sized.
• The PR contains an idempotent DB migration.
• I have verified the correctness of the DB migration using relevant data (e.g. test-generated data).
• New code has enough tests.
• New code has enough documentation to answer "how do I use it?" and "what does it do?".
• Existing documentation is up-to-date, if impacted.

[bryanchriswhite]

Thanks @MissingNO57! 🙌