rustfmt: format the codebase with nightly-2024-07-16
The CI has moved to a newer nightly, which slightly changes how it wraps
comments (which is the very option we use nightly for).
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}