[mypy] Add mypy type annotation part 1 (#4006)

pyproject.toml

@@ -46,10 +46,13 @@ ignore = [
 python_version = "3.8"
 
 ignore_missing_imports = true
+ check_untyped_defs = true
 
 files = "vllm"
 # TODO(woosuk): Include the code from Megatron and HuggingFace.
-exclude = "vllm/model_executor/parallel_utils/|vllm/model_executor/models/"
+exclude = [
+    "vllm/model_executor/parallel_utils/|vllm/model_executor/models/",
+]
 
 
 [tool.codespell]