Handle non-serializable objects in vllm bench (vllm-project#21665)

Author: huydhn

utils.py

@@ -67,4 +67,9 @@ def iterencode(self, o: Any, *args, **kwargs) -> Any:
 
 def write_to_json(filename: str, records: list) -> None:
     with open(filename, "w") as f:
-        json.dump(records, f, cls=InfEncoder)
+        json.dump(
+            records,
+            f,
+            cls=InfEncoder,
+            default=lambda o: f"<{type(o).__name__} is not JSON serializable>",
+        )