now associating a dewar to a slot with checks that it is not associated to another slot

backend/app/routers/logistics.py

@@ -98,6 +98,12 @@ async def refill_dewar(qr_code: str, db: Session = Depends(get_db)):
 
     # Process refill
     dewar.last_refill = datetime.now()
+
+    # Calculate and update time until next refill
+    time_until_refill_seconds = calculate_time_until_refill(dewar.last_refill)
+    db.query(SlotModel).filter(SlotModel.dewar_unique_id == dewar.unique_id).update(
+        {'time_until_refill': time_until_refill_seconds})
+
     new_event = LogisticsEventModel(
         dewar_id=dewar.id, slot_id=None,  # No specific slot, as it's a refill event
         event_type="refill",