transaction: fix __repr__() and make the default name bytes
This likely was always wrong on py3, since going back to
aff5996f3043, these
were added as a r-strings. Callers seem to always be supplying bytes, which
makes the `b'/'.join(...)` part OK, but then bytes can't be interpolated into
str with "%s", so it wouldn't have worked in either case.
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}