Add account deletion scheduler and comprehensive tests

- Implemented account deletion scheduler in `account_deletion_scheduler.py` to manage user deletions based on a defined threshold.
- Added logging for deletion processes, including success and error messages.
- Created tests for deletion logic, including edge cases, retry logic, and integration tests to ensure complete deletion workflows.
- Ensured that deletion attempts are tracked and that users are marked for manual intervention after exceeding maximum attempts.
- Implemented functionality to check for interrupted deletions on application startup and retry them.

backend/models/user.py

@@ -18,6 +18,8 @@ class User(BaseModel):
     pin_setup_code_created: str | None = None
     marked_for_deletion: bool = False
     marked_for_deletion_at: str | None = None
+    deletion_in_progress: bool = False
+    deletion_attempted_at: str | None = None
 
     @classmethod
     def from_dict(cls, d: dict):
@@ -37,6 +39,8 @@ class User(BaseModel):
             pin_setup_code_created=d.get('pin_setup_code_created'),
             marked_for_deletion=d.get('marked_for_deletion', False),
             marked_for_deletion_at=d.get('marked_for_deletion_at'),
+            deletion_in_progress=d.get('deletion_in_progress', False),
+            deletion_attempted_at=d.get('deletion_attempted_at'),
             id=d.get('id'),
             created_at=d.get('created_at'),
             updated_at=d.get('updated_at')
@@ -60,6 +64,8 @@ class User(BaseModel):
             'pin_setup_code': self.pin_setup_code,
             'pin_setup_code_created': self.pin_setup_code_created,
             'marked_for_deletion': self.marked_for_deletion,
-            'marked_for_deletion_at': self.marked_for_deletion_at
+            'marked_for_deletion_at': self.marked_for_deletion_at,
+            'deletion_in_progress': self.deletion_in_progress,
+            'deletion_attempted_at': self.deletion_attempted_at
         })
         return base