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