/// let listeners = vec![
/// (monitor_block_hash, &mut monitor_listener as &mut dyn chain::Listen),
/// (manager_block_hash, &mut manager as &mut dyn chain::Listen),
/// let listeners = vec![
/// (monitor_block_hash, &mut monitor_listener as &mut dyn chain::Listen),
/// (manager_block_hash, &mut manager as &mut dyn chain::Listen),