typing: add type hints to bdiff implementations...
typing: add type hints to bdiff implementations
Not super important code, but this was an exercise in using `merge-pyi` to fold
type stubs back into the code on something small. The cext stubs don't seem to
be getting used (at least the only thing in `.pytype/pyi/mercurial/cext` after a
run generating the stubs is `__init__.pyi`), so maybe this will help some.