delta-find: move filing of some debug data in `_one_dbg_data`
Since the `_one_dbg_data` method is meant to create a valid debug dictionnary.
We can as well prefill the relevant value to reduce the amount of debug code in
the main code.
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}