fix(streaming): avoid duplicate chunk on cancel race in _put

When fut.cancel() returns False the coroutine already completed and
the item is in the queue. Previously the loop would continue and
enqueue the same item again. Now we return immediately when cancel
fails, preventing duplicate chunks under tight timing.

litellm/litellm_core_utils/streaming_handler.py

@@ -109,7 +109,8 @@ class _SyncIteratorToQueue:
                 fut.result(timeout=0.5)
                 return
             except TimeoutError:
-                fut.cancel()
+                if not fut.cancel():
+                    return
                 continue
             except Exception:
                 return