Enforce types

[ColeDCrawford]

Next step after #11 is to enforce types to a greater or lesser degree with something like MyPy or Pydantic. Here's a list of options: https://github.com/ethanhs/python-typecheckers.

I don't have much personal experience with any of the above options; I use pyright through pylance in VS Code as the default,. I've heard the most about mypy and pydantic. pytype also looks intriguing. Maybe a spike to explore the top few options and then implement in precommit and CI?

• [x] manually run a checker and clean up types in the code
• [x] preliminary mypy checking in CI ; documented in readme but not otherwise enforced
• [x] implement pre-commit check