ADR suggestion: New code should use type hints

[rozyczko]

As discussed during the code camp (07/01/2025) we are trying to move towards having type-hints in the code.
Before addressing the bulk of the code, we should start requiring all the new code to contain type hints for all method signatures.
Checking type hints should also be a part of the code review.

[krzywon]

If we implement ruff as in #3171, this might happen automatically...