docs: public void addOnTransactionBroadcastListener(Executor executor, OnTransactionBroadcastListener listener) {
          peersTransactionBroadastEventListeners.add(new ListenerRegistration<>(checkNotNull(listener), executor));
          for (Peer peer : getConnectedPeers())
              peer.addOnTransactionBroadcastListener(executor, listener);
          for (Peer peer : getPendingPeers())
              peer.addOnTransactionBroadcastListener(executor, listener);
      }