[Doc] Add typing hints / mypy types cleanup (#3816)

Co-authored-by: Roger Wang <136131678+ywang96@users.noreply.github.com>

vllm/transformers_utils/config.py

@@ -1,10 +1,10 @@
-from typing import Optional
+from typing import Dict, Optional
 
 from transformers import AutoConfig, PretrainedConfig
 
 from vllm.transformers_utils.configs import *
 
-_CONFIG_REGISTRY = {
+_CONFIG_REGISTRY: Dict[str, PretrainedConfig] = {
     "chatglm": ChatGLMConfig,
     "dbrx": DbrxConfig,
     "mpt": MPTConfig,