[Refactor] [6/N] to simplify the vLLM openai chat_completion serving architecture (#32240)

Signed-off-by: chaunceyjiang <chaunceyjiang@gmail.com>

tests/entrypoints/openai/utils.py

@@ -4,11 +4,13 @@ import json
 from collections.abc import AsyncGenerator
 from typing import Any
 
-from vllm.entrypoints.openai.protocol import (
+from vllm.entrypoints.openai.chat_completion.protocol import (
     ChatCompletionResponse,
     ChatCompletionResponseChoice,
     ChatCompletionStreamResponse,
     ChatMessage,
+)
+from vllm.entrypoints.openai.engine.protocol import (
     UsageInfo,
 )