rust-update: make `update_from_null` respect `worker.numcpu` config option This was overlooked in the original series. This is important for tests (because we run many at once), and for the occasional end user that wants to keep their CPU usage in check. A future series should clean up this `worker` parameter tunelling business by rewriting the config in Rust, but doing so on stable would be a very bad idea.

pub mod dirstate_map;
pub mod on_disk;
pub mod owning;
pub mod path_with_basename;
pub mod status;