Draft: typing: make the filelog class known to pytype
This fails in CI with pytype 2023.06.16, which I can't setup locally in py3.8 due to "ModuleNotFoundError: No module named 'pybind11'", and can't create a venv in py3.7 locally. 2024.04.11 runs locally fail for other reasons, so splitting this off for now and parking it.