Refactor duty authentication and event type handling

- Introduced a new function `get_authenticated_username` to centralize Mini App authentication logic, improving code readability and maintainability.
- Updated the duty fetching logic to map unknown event types to "duty" for consistent API responses.
- Enhanced the `get_duties` function to include duties starting on the last day of the specified date range.
- Improved session management in the database layer to ensure rollback on exceptions.
- Added tests to validate the new authentication flow and event type handling.

handlers/group_duty_pin.py

@@ -118,7 +118,8 @@ async def _schedule_next_update(
     for job in job_queue.get_jobs_by_name(name):
         job.schedule_removal()
     if when_utc is not None:
-        delay = when_utc - datetime.utcnow()
+        now_utc = datetime.now(timezone.utc).replace(tzinfo=None)
+        delay = when_utc - now_utc
         if delay.total_seconds() < 1:
             delay = 1
         job_queue.run_once(