390 mypy

[saeliddp]

Context

#390 -- the goal of this PR is to add a type checker to our CI. We settled on mypy, which seems to be widely used and comes recommended by Philip.

The changes related to adding mypy to CI are just in test_lint.yaml and pyproject.toml. The rest of the changes are fixing files so that they pass the mypy checks.

The majority of type fixes fall into these categories:

1. we just forgot to add the type hints
2. we did not handle the possible None type of variables that are typed Optional[<something>]
3. we didn't use the full path for Qt enums (e.g. we would have Qt.AlignTop instead of Qt.AlignmentFlag.AlignTop). Not sure why exactly this was working, but seems to be fine either way.

[yrkim98]

this was a huge refactor- thank you
Did you replace all instances of Dict and List with builtin types?

[saeliddp]

Did you replace all instances of Dict and List with builtin types?

I replaced them where I saw them, but I wasn't specifically looking for it, so I'm sure a couple slipped by