fix(serving_chat): shallow copy bug — [[]] * n and [parser] * n share references

When n>=2, all_previous_token_ids entries pointed to the SAME list,
so appending tokens for choice 0 corrupted choice 1's history.
Same for tool_parsers: all choices shared one stateful parser instance.

Changed to list comprehensions that create independent objects.

Found via CCCL result_policy.cuh read: distributed result delivery
requires isolated per-rank state — same principle applies to
per-choice token tracking in vLLM streaming.

qwen3_6_scripts/serving_chat.py

@@ -348,7 +348,7 @@ class OpenAIServingChat(OpenAIServing):
         # parsing and reasoning parsing (both require full-history context).
         if tool_choice_auto or use_reasoning:
             previous_texts = [""] * num_choices
-            all_previous_token_ids = [[]] * num_choices
+            all_previous_token_ids = [[] for _ in range(num_choices)]
         else:
             previous_texts, all_previous_token_ids = None, None
 
@@ -357,7 +357,8 @@ class OpenAIServingChat(OpenAIServing):
             if tool_choice_auto and self.tool_parser:
                 tool_parsers: List[Optional[ToolParser]] = [
                     self.tool_parser(tokenizer)
-                ] * num_choices
+                    for _ in range(num_choices)
+                ]
             else:
                 tool_parsers = [None] * num_choices
         except RuntimeError as e: