[Python] Use type hints everywhere possible

Having types explicitly spelled out helps with code readability and debugging. I think we should try to use it in any python code we produce and convert old code to do the same.

The issue does not name files, tests, or a defined scope. Start by inventorying the repository's Python code and determining which files are covered, then agree on what “everywhere possible” means before making changes. Done would require explicit type hints across the agreed scope and verification that the Python code still works.

Written by the indexing model from the issue text.