.arcconfig

util: add method to peek item in lrucachedict

I want a function that doesn't unnecessarily update the internal state of
the cache dict after fork().

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