Clean stub files up and have automated checks

[rayzchen]

• Make mypy work with PyUnity
• Finish stub files
• Identify stub problems
• Check stub file and source code compatability
• Fix stubtest
• Automate mypy
• Automate stubtest

[rayzchen]

stubs/generate.py does quite a good job but needs human checking and relies on the coverage of tests/.

[rayzchen]

Need a better way to check number of arguments or argument names are correct

[rayzchen]

Investigating mypy and stubtest. Currently facing issues with

pyunity/stubs/pyunity/loader.pyi

Line 79 in ec7fa8d

savers: Dict[Type[AT], Callable[[AT, Project, Union[str, Path]], None]] = ...

which could be fixed by replacing AT with Asset but won't denote the relationship between the key and the argument. stubtest is also not finding module exports from submodules, but interestingly also seems to not be able to import a simple package structure (see https://github.com/rayzchen/stubtest-bug).

[rayzchen]

Typechecking is almost completely automated, all which is lacking is a GitHub Actions workflow.

[rayzchen]

Waiting for Mypy 1.4.0 to release, hopefully with the bugfix for python/mypy#15397.

[rayzchen]

fee9190 implements mypy testing in ci

[rayzchen]

Awaiting python/mypy#15300 to be fixed

[rayzchen]

Currently stubtest succeeds with an ignorefile that ignores __all__, since packages extend it with the __all__ from submodules but stubtest cannot detect that.