[Refactor] Relocate completion and chat completion tests (#37125)

Signed-off-by: sfeng33 <4florafeng@gmail.com>

tests/entrypoints/llm/test_mm_cache_stats.py

@@ -6,13 +6,12 @@ import logging
 import pytest
 import regex as re
 
+from tests.entrypoints.openai.chat_completion.test_vision import TEST_IMAGE_ASSETS
 from vllm import LLM
 from vllm.entrypoints.chat_utils import ChatCompletionMessageParam
 from vllm.v1.metrics import loggers as stat_loggers
 from vllm.v1.metrics.reader import Counter, Metric
 
-from ..openai.test_vision import TEST_IMAGE_ASSETS
-
 
 def _make_messages(image_url: str) -> list[ChatCompletionMessageParam]:
     return [