rust: use the new `UncheckedRevision` everywhere applicable This step converts all revisions that shouldn't be considered "valid" in any context to `UncheckedRevison`, allowing `Revision` to be changed for a stronger type in a later changeset. Note that the conversion from unchecked to checked is manual and requires at least some thought from the programmer, although directly using `Revision` is still possible. A later changeset will make this mistake harder to make.