Refactor scheduled task repository and schemas for improved type hints and consistency

- Updated type hints from List/Optional to list/None for better readability and consistency across the codebase.
- Refactored import statements for better organization and clarity.
- Enhanced the ScheduledTaskBase schema to use modern type hints.
- Cleaned up unnecessary comments and whitespace in various files.
- Improved error handling and logging in task execution handlers.
- Updated test cases to reflect changes in type hints and ensure compatibility with the new structure.

tests/conftest.py

@@ -351,11 +351,11 @@ async def admin_cookies(admin_user: User) -> dict[str, str]:
 
 @pytest.fixture
 def test_user_id(test_user: User):
-    """Get test user ID.""" 
+    """Get test user ID."""
     return test_user.id
 
 
-@pytest.fixture  
+@pytest.fixture
 def test_sound_id():
     """Create a test sound ID."""
     import uuid
@@ -364,7 +364,7 @@ def test_sound_id():
 
 @pytest.fixture
 def test_playlist_id():
-    """Create a test playlist ID.""" 
+    """Create a test playlist ID."""
     import uuid
     return uuid.uuid4()