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/test_scheduled_task_model.py

@@ -3,8 +3,6 @@
 import uuid
 from datetime import datetime, timedelta
 
-import pytest
-
 from app.models.scheduled_task import (
     RecurrenceType,
     ScheduledTask,
@@ -217,4 +215,4 @@ class TestScheduledTaskModel:
         assert RecurrenceType.WEEKLY == "weekly"
         assert RecurrenceType.MONTHLY == "monthly"
         assert RecurrenceType.YEARLY == "yearly"
-        assert RecurrenceType.CRON == "cron"
+        assert RecurrenceType.CRON == "cron"