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

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

tests/conftest.py

@@ -60,7 +60,7 @@ from vllm.multimodal.utils import fetch_image
 from vllm.outputs import RequestOutput
 from vllm.sampling_params import BeamSearchParams
 from vllm.transformers_utils.utils import maybe_model_redirect
-from vllm.utils.collections import is_list_of
+from vllm.utils.collection_utils import is_list_of
 from vllm.utils.torch_utils import set_default_torch_num_threads
 
 logger = init_logger(__name__)