Add ty type checker alongside mypy

- Add ty to dev dependencies
- Add [tool.ty.environment] config in pyproject.toml
- Add ty check step to CI workflow
- Fix type error in client.py that ty found but mypy missed:
  subprocess.Popen.stdout is typed as IO[bytes] but BufferedReader
  expects RawIOBase, requiring an explicit cast

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: rustyconover

.github/workflows/ci.yml

@@ -49,5 +49,8 @@ jobs:
       - name: Check linting
         run: uv run ruff check .
 
-      - name: Type check
+      - name: Type check (mypy)
         run: uv run mypy vgi/
+
+      - name: Type check (ty)
+        run: uv run ty check vgi/

pyproject.toml

@@ -42,6 +42,9 @@ warn_unused_ignores = true
 module = "structlog.*"
 ignore_missing_imports = true
 
+[tool.ty.environment]
+python-version = "3.12"
+
 [tool.pytest.ini_options]
 addopts = "--mypy --ruff"
 testpaths = ["tests"]
@@ -50,4 +53,5 @@ testpaths = ["tests"]
 dev = [
     "lxml>=6.0.2",
     "pytest-timeout>=2.4.0",
+    "ty>=0.0.8",
 ]

uv.lock

@@ -1255,7 +1255,7 @@ def start(self) -> None:
             )
             self._stderr_thread.start()
 
-        self._stdout_buffered = io.BufferedReader(self._proc.stdout)
+        self._stdout_buffered = io.BufferedReader(cast(io.RawIOBase, self._proc.stdout))
         assert self._proc.stdin is not None, "stdin pipe not created for worker"
         self._stdin_sink = pa.PythonFile(cast(io.IOBase, self._proc.stdin))