Introduction of static type checking

[a-alak]

As type annotations and static type checking is more broadly used in the python ecosystem i thought it might be a good idea to at least consider the level of support for type annotation wanted in this repo.

There is clearly interest in this, as PR #755 and PR #771 is introducing type upgrades (both not merged yet).

I am creating this issue to open a discussion on what this packages type annotation plan is.

Some considerations:

• Should static type checking be added to CI?
• Which type checkers to support? Ecosystem is broad now, and there is subtle differences between the major solutions (mypy, pyright, ty and pyrefly). PR feat: Add correct types and make mypy --strict pass #771 is checked against mypy --strict, and added it to the makefile.

Would love to contribute if the maintainers think it is something worth adding.