Add comprehensive tests for scheduled task repository, scheduler service, and task handlers

- Implemented tests for ScheduledTaskRepository covering task creation, retrieval, filtering, and status updates.
- Developed tests for SchedulerService including task creation, cancellation, user task retrieval, and maintenance jobs.
- Created tests for TaskHandlerRegistry to validate task execution for various types, including credit recharge and sound playback.
- Ensured proper error handling and edge cases in task execution scenarios.
- Added fixtures and mocks to facilitate isolated testing of services and repositories.

app/models/__init__.py

@@ -1 +1,32 @@
 """Models package."""
+
+# Import all models for SQLAlchemy metadata discovery
+from .base import BaseModel
+from .credit_action import CreditAction
+from .credit_transaction import CreditTransaction
+from .extraction import Extraction
+from .favorite import Favorite
+from .plan import Plan
+from .playlist import Playlist
+from .playlist_sound import PlaylistSound
+from .scheduled_task import ScheduledTask
+from .sound import Sound
+from .sound_played import SoundPlayed
+from .user import User
+from .user_oauth import UserOauth
+
+__all__ = [
+    "BaseModel",
+    "CreditAction",
+    "CreditTransaction",
+    "Extraction",
+    "Favorite", 
+    "Plan",
+    "Playlist",
+    "PlaylistSound",
+    "ScheduledTask",
+    "Sound",
+    "SoundPlayed",
+    "User",
+    "UserOauth",
+]