rust-index: honour incoming using_general_delta in `deltachain`
It looks to be a leftover from some past, but the C index considers
only the value passed from Python whereas up to now the Rust index
was using the value of its attribute.
As a middle ground, we make this argument of `deltachain` optional from
the Python side, with the Rust implementation only defaulting to its
attribute. This way, we reduce false leads when a difference in results
is spotted.
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}