rust: normalize `_for_unchecked_rev` naming among revlogs and the index This normalizes the naming scheme between the `Revlog`, `Changelog`, etc. which is less suprising, though no real bugs could stem from this because of the type signature mismatch. The very high-level `Repo` object still uses an `UncheckedRevision` parameter for its methods because that's what most callers will want.