.arcconfig

tags-fnode-cache: do not repeatedly open the filelog in a loop

While getting multiple hgtagsfnodecache entries, we were opening (and closing)
the `.hgtags` filelog for each iteration. The meant repeatedly reading and
parsing the version same information from disk. A quite costly operation.

We no longer do this, leading to a sizable improvement in `hg debugupdatecache`
run for an already warm repositories.

### data-env-vars.name           = mercurial-2018-08-01-zstd-sparse-revlog
  # benchmark.name               = debug-update-cache
  # benchmark.variants.pre-state = warm
before:  1.711778 seconds
after:   0.213229 seconds  (-87.54%)
  # data-env-vars.name           = pypy-2018-08-01-zstd-sparse-revlog
before:  4.010817 seconds
after:   0.381141 seconds  (-90.50%)
  # data-env-vars.name           = netbeans-2018-08-01-zstd-sparse-revlog
before: 13.574141
after:   1.023007 seconds  (-92.46%)
  # data-env-vars.name           = mozilla-central-2018-08-01-zstd-sparse-revlog
before: 18.884656
after:   1.465735 seconds  (-92.24%)
  # data-env-vars.name           = mozilla-try-2019-02-18-zstd-sparse-revlog
before: 88.924823
after:   6.511771 seconds  (-92.68%)

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