[CI/Build] mypy: check vllm/inputs

Enable `mypy` checks on `vllm/inputs` and add some casts to fix the
warnings present for this directory.

Part of issue vllm-project#3680

Signed-off-by: Russell Bryant <rbryant@redhat.com>

tools/mypy.sh

@@ -21,7 +21,7 @@ run_mypy vllm/distributed
 run_mypy vllm/engine
 run_mypy vllm/entrypoints
 run_mypy vllm/executor
-#run_mypy vllm/inputs
+run_mypy vllm/inputs
 run_mypy vllm/logging
 run_mypy vllm/lora
 run_mypy vllm/model_executor

vllm/inputs/parse.py

@@ -1,4 +1,4 @@
-from typing import List, Literal, Sequence, TypedDict, Union, overload
+from typing import List, Literal, Sequence, TypedDict, Union, cast, overload
 
 from typing_extensions import TypeIs
 
@@ -44,13 +44,16 @@ def parse_and_batch_prompt(
 
         if is_list_of(prompt, str):
             # case 2: array of strings
+            prompt = cast(List[str], prompt)
             return [
                 ParsedText(content=elem, is_tokens=False) for elem in prompt
             ]
         if is_list_of(prompt, int):
             # case 3: array of tokens
+            prompt = cast(List[int], prompt)
             return [ParsedTokens(content=prompt, is_tokens=True)]
         if is_list_of(prompt, list):
+            prompt = cast(List[List[int]], prompt)
             if len(prompt[0]) == 0:
                 raise ValueError("please provide at least one prompt")