typing: run `merge-pyi` on `mercurial/vfs.py` The *.pyi file was generated with pytype 2023.11.21. There were a few things here that were wrong (e.g. `writelines()` takes an `Iterable[bytes]`, not `bytes`, or inexplicable errors like importing several of the vfs classes from this very module), and those changes have been dropped manually here.