fix pre-commit hook and code quality fixes

backend/routes/booking.py

@@ -1,5 +1,6 @@
 """Booking routes for users to book appointments."""
 
+from collections.abc import Sequence
 from datetime import UTC, date, datetime, time, timedelta
 
 from fastapi import APIRouter, Depends, HTTPException, Query
@@ -86,7 +87,7 @@ def _validate_booking_date(d: date) -> None:
 
 
 def _expand_availability_to_slots(
-    availability_slots: list[Availability],
+    availability_slots: Sequence[Availability],
     target_date: date,
 ) -> list[BookableSlot]:
     """Expand availability time ranges into 15-minute bookable slots."""