Apply type annotations

[ehrenb]

Applied type annotations to much of the code-base. May want to squash commits as there are a lot of redundant messages in the log..See more detailed notes below.

• For optional values, I used the syntax Union[type,None] over type|None to keep changes compatible with Python3.9+. Optional[type] could also been used here.
• In some modules, circular imports occur when a module requires another (and vice versa) for a type hint. To avoid this error, I use from __future__ import annotations which postpones evaluation of annotations and still allows for hints to be type names rather than strings.
  • https://adamj.eu/tech/2021/05/15/python-type-hints-future-annotations/
  • https://adamj.eu/tech/2021/05/13/python-type-hints-how-to-fix-circular-imports/
  • https://peps.python.org/pep-0563/#abstract
• Added TYPE_CHECKING checks to allow future static type checkign tools to run, such as mypy

[erev0s]

Thank you @ehrenb! Nicely done and well structured