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/events/types/event_types.py

@@ -15,3 +15,4 @@ class EventType(Enum):
     CHILD_MODIFIED = "child_modified"
 
     USER_MARKED_FOR_DELETION = "user_marked_for_deletion"
+    USER_DELETED = "user_deleted"

backend/events/types/user_deleted.py

@@ -0,0 +1,26 @@
+from events.types.payload import Payload
+
+
+class UserDeleted(Payload):
+    """
+    Event payload for when a user account is deleted.
+    This event is broadcast only to admin users.
+    """
+    def __init__(self, user_id: str, email: str, deleted_at: str):
+        super().__init__({
+            'user_id': user_id,
+            'email': email,
+            'deleted_at': deleted_at,
+        })
+
+    @property
+    def user_id(self) -> str:
+        return self.get("user_id")
+
+    @property
+    def email(self) -> str:
+        return self.get("email")
+
+    @property
+    def deleted_at(self) -> str:
+        return self.get("deleted_at")