Restore proper cancel functionality

- Revert stopping criteria to check cancel_event.is_set()
- Confirmed stopping criteria mechanism works (generation stopped after 1 token in test)
- Cancel should now work properly, stopping generation after current token when clicked

app.py

@@ -28,7 +28,7 @@ cancel_event = threading.Event()
 # ------------------------------
 class CancelStoppingCriteria(StoppingCriteria):
     def __call__(self, input_ids, scores, **kwargs):
-        return True
+        return cancel_event.is_set()
 
 # ------------------------------
 # Torch-Compatible Model Definitions with Adjusted Descriptions