Function handle_events 

pub async fn handle_events<F, R, E>(
    db: Database,
    tracker: DynEventLogTracker,
    log_event_added: Receiver<()>,
    call_fn: F,
) -> Result<(), EventHandlerError<E>>
where
    F: Fn(&mut DatabaseTransaction<'_, NonCommittable>, EventLogEntry) -> R,
    R: Future<Output = Result<(), E>>,
    E: Error + 'static,

Feeds every entry of the event log, past and future, to call_fn.

tracker remembers how far the log has been read so a restart resumes where it left off; the loop stops when call_fn fails or the client shuts down.