rust-revlog: bare minimal NodeTree exposition The independent `NodeTree` instances needs to be associated to an index (for forward-checks of candidates) but do not need to encompass all revisions from that index. This is exactly how it is used in `scmutil.shortesthenodeidprefix` and we restrict the implementation to the bare minimum needed there and to write convincing tests. It would of course be fairly trivial to add more.

{
    "conduit_uri": "https://phab.mercurial-scm.org/api",
    "phabricator.uri": "https://phab.mercurial-scm.org/",
    "repository.callsign": "HG",
    "arc.land.onto.default": "@",
    "base": "hg:.^"
}