Resolve problems and warnings from static code analysis.

[LuukBlom]

Description

We use Pylance to do some static code analysis, which produces a huge amount of warnings and problems, that we kind of ignore.

Lets at least tackle the easy ones: Add type hints everywhere, checking for None, type mismatches etc.
It should prevent bugs we have not had yet.

Since this is a huge amount of work, I think the bests approach to keep track of it all, is to go through the codebase per feature or even per file.
Then, when you find a feature or file you want to resolve the warnings for:
add a small issue for that feature/file, and add it in the issue list of below.

Issue list

#xxx this is an example feature

Use case

No response