rust: remove unused error variant All paths check that the working directory revision is not used.

rust: add `UncheckedRevision` type This is the start of a series whose aim is to separate "checked" and "unchecked" revision numbers. A "checked" revision number is valid for a given index, allowing us to have faster algorithms that don't do redundant checks all the time and have a clearer view of the kinds of revisions we're working with.

debugwireproto: migrate `opts` to native kwargs