fix(regression): clone from reference items (#18662)

Signed-off-by: Aaron Pham <[email protected]>

Author: aarnphm

vllm/sequence.py

@@ -1494,7 +1494,7 @@ def add_request(request_id: str, engine, params, **kwargs):
         for i in range(original_params.n):
             request_id_i = f"{request_id}_parallel_sample_{i}"
             group.seq_id_to_index[request_id_i] = i
-            params = params.clone()
+            params = original_params.clone()
             params.n = 1
             if params.seed is not None:
                 params.seed += i