[v2] Add typechecker

[Samoed]

Currently, we have a lot of # type: ignore comments but haven’t specified a type checker. In the v2 branch, we've added more type annotations in most places, and I think we could introduce mypy (or ty, once it reaches at least version 0.0.1). However, I'm unsure about the configuration—if we set it to strict, we might end up with too many errors to resolve easily.

Also maybe soon v2 version of mypy will be released python/mypy#17967

[KennethEnevoldsen]

It sounds like ty might be what we should go for. I don't want to add it before it is stable, though. We could, however, add it to the makefile (before adding it to the CI)

edit: Some initial testing showed that we will probably need to wait a bit before we adopt ty.