typing: align the signatures of `repository.ifilestorage` overrides This is the same as 048c11993d6a for `imanifestrevisionstored`, with the same belated realization about missing the Protocol marker. Since I've been jumping around to the various subclasses and copying extant hints to places where they're missing, do that here too. This also covers the 3 interfaces subclassed by `repository.ifilestorage` (`repository.ifileindex`, `repository.ifiledata`, and `repository.ifilemutation`). Obviously the whole base class needs hints, but I don't want to get side tracked here- it doesn't look like any of the implementing classes have any additional hints.