Fixes: 1) Correct `urlsafe_base64_encode` decoding logic in tests; 2) Fix queryset access issues in resolvers; 3) Address missing or incorrect imports across multiple files.
Extra: Improve code readability with consistent naming and formatting; Add `# noinspection` annotations to suppress IDE warnings; Update `pyproject.toml` to exclude `drf.py` in MyPy checks.
Fixes: 1) Add missing import for `transaction` in `signals.py`; 2) Fix incorrect handling of `pre_save` skip logic for non-existent users; 3) Correct conditional logic for email change handling to avoid unnecessary activation resets.
Extra: 1) Simplify mutation attribute validation in `mutations.py` by excluding specific fields earlier in the loop; 2) Improve code readability with minor refactors in both `signals.py` and `mutations.py`.
