Function mz_stash::transaction::maybe_update_antichain

fn maybe_update_antichain(
    map: &Arc<Mutex<BTreeMap<i64, Antichain<Timestamp>>>>,
    id: i64,
    updated: Antichain<Timestamp>
)

Updates an antichain cache if the new value has advanced. Needed because the functions here are often called in try_joins where the futures execute in unknown order and we want to prevent a race condition poisioning the cache by going backward.