Add type hints to the codebase

[scootermon]

This PR adds type hints to the codebase without making any other changes.
There are a few type errors that get picked up by the likes of mypy, ty, pyright, but resolving those requires changes to the code, which I wanted to avoid in this PR.

I tested the scripts with Python 3.9 (the min version as per the project.toml) to verify it still works.

[qkaiser]

That's a good first step. We want to get stronger type checking in place in the scope of #79

We'll try to review this in the coming days, thanks for contributing !

[e3krisztian]

It is a nice PR, I think it should be merged.

Although I added some comments, those are very minor and kind of nitpicking looking at the size of changes.

[e3krisztian]

Thanks for the update!
I have found this new "problem", I have skipped over earlier, but otherwise, it looks very good!

I would split off _LayoutPair(?) from _LayoutInfo, and revert the code change in associate_blocks - only casting the result in the return. I think it would result in new typing problem in associate_blocks, but that should be OK - a reminder to fix it later.

[e3krisztian]

Thanks!