Add static typing

[Tim Hutt]

As far as I can tell this is missing static types or type stubs.

The best way to do it is to add type hints into the code, then you have to add an empty py.typed file in your package (next to __init__.py).

I would recommend using Pyright over Mypy. It's much better. The easiest way to run/enforce it is using the Pyright pre-commit hook.

[Jonathon Reinhart]

I think this is a duplicate of #371.