refactor: improve backend type safety and import organization

- Add TYPE_CHECKING guards for runtime-expensive imports (aiohttp, aiosqlite)
- Reorganize imports to follow PEP 8 conventions
- Convert TypeAlias to modern PEP 695 type syntax (where appropriate)
- Use Sequence/Mapping from collections.abc for type hints (covariant)
- Replace string literals with cast() for improved type inference
- Fix casting of Fail2BanResponse and TypedDict patterns
- Add IpLookupResult TypedDict for precise return type annotation
- Reformat overlong lines for readability (120 char limit)
- Add asyncio_mode and filterwarnings to pytest config
- Update test fixtures with improved type hints

This improves mypy type checking and makes type relationships explicit.

backend/tests/test_services/test_auth_service.py

@@ -73,7 +73,7 @@ class TestCheckPasswordAsync:
             auth_service._check_password("secret", hashed),  # noqa: SLF001
             auth_service._check_password("wrong", hashed),  # noqa: SLF001
         )
-        assert results == [True, False]
+        assert tuple(results) == (True, False)
 
 
 class TestLogin: