[Misc] Move utils to avoid conflicts with stdlib, and move tests (#27169)

Signed-off-by: DarkLight1337 <tlleungac@connect.ust.hk>

tests/models/multimodal/generation/vlm_utils/model_utils.py

@@ -25,7 +25,7 @@ from transformers import (
 from transformers.video_utils import VideoMetadata
 
 from vllm.logprobs import SampleLogprobs
-from vllm.utils.collections import is_list_of
+from vllm.utils.collection_utils import is_list_of
 
 from .....conftest import HfRunner, ImageAsset, ImageTestAssets
 from .types import RunnerOutput