templatekw: cache mergestate even if merge is not ongoing While playing with eBPF, I noticed .hg/merge/state{,2} files were tried to open() for each revision. That's not healthy. Let's cache the "inactive" state as well.

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