Function partition_backoffs 

pub(super) async fn partition_backoffs<T>(
    context: &Context<'_>,
    prepared: &Prepared,
    backoffs: &BTreeMap<OwnedServerName, PeerBackoff>,
    now: u64,
) -> (Vec<OwnedServerName>, Vec<Outcome<T>>)

Splits the room’s destinations into dispatchable origins and held origins.

An origin still inside its peer backoff at now becomes a Fault::Backoff outcome with zero elapsed time instead of a destination.