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.
