_internal(fix[async_subprocess]): Fix mypy type errors and formatting

why: Ensure Phase 1 passes full verification pipeline
what:
- Add None checks before .strip() calls on result.stdout in tests
- Apply ruff formatting to list comprehension in _args_as_list()

Author: tony

tests/_internal/test_async_subprocess.py

@@ -187,6 +187,7 @@ async def test_run_with_cwd(self, tmp_path: Path) -> None:
         cmd = AsyncSubprocessCommand(args=["pwd"], cwd=tmp_path)
         result = await cmd.run(text=True)
 
+        assert result.stdout is not None
         assert result.stdout.strip() == str(tmp_path)
 
     @pytest.mark.asyncio
@@ -228,5 +229,6 @@ async def test_concurrent_commands(self) -> None:
 
         assert len(results) == 5
         for i, result in enumerate(results):
+            assert result.stdout is not None
             assert result.stdout.strip() == str(i)
             assert result.returncode == 0