docs: public int layerSize(String layerName) {
          Layer l = getLayer(layerName);
          if(l == null){
              throw new IllegalArgumentException("No layer with name \"" + layerName + "\" exists");
          }
          org.deeplearning4j.nn.conf.layers.Layer conf = l.conf().getLayer();
          if (conf == null || !(conf instanceof FeedForwardLayer)) {
              return 0;
          }
          FeedForwardLayer ffl = (FeedForwardLayer) conf;
  
          // FIXME: int cast
          return (int) ffl.getNOut();
      }