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.

app/core/database.py

@@ -4,11 +4,11 @@ from sqlalchemy.ext.asyncio import AsyncEngine, create_async_engine
 from sqlmodel import SQLModel
 from sqlmodel.ext.asyncio.session import AsyncSession
 
+# Import all models to ensure SQLModel metadata discovery
+import app.models  # noqa: F401
 from app.core.config import settings
 from app.core.logging import get_logger
 from app.core.seeds import seed_all_data
-# Import all models to ensure SQLModel metadata discovery
-import app.models  # noqa: F401
 
 engine: AsyncEngine = create_async_engine(
     settings.DATABASE_URL,