Typecheck some API interfaces

[mfisher87]

I'm going to be changing a lot in the refactor to use Harmony. The typechecker is going to help find sneaky bugs along the way. This is a start, but I'd really like feedback.

My main goal here is to avoid refactoring the code more than needed and set the stage for future cleanups and refactors. E.g. I think long-term, we will want to split up the Parameters class instead of having it handle all the kinds of parameters.

I'm using pyright here for the first time, and I'm pleased with it compared to Mypy so far. The reason I switched to Pyright: https://github.com/python/mypy/issues/12098