Tidy vllm/config/__init__.py to only add classes and functions (#26405)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

vllm/model_executor/layers/mamba/mamba_utils.py

@@ -4,7 +4,8 @@ from typing import Union
 
 import torch
 
-from vllm.config import MambaDType, ModelDType
+from vllm.config.cache import MambaDType
+from vllm.config.model import ModelDType
 from vllm.distributed import divide
 from vllm.utils import STR_DTYPE_TO_TORCH_DTYPE, get_kv_cache_torch_dtype