@Override
  public void finish(String sourceName, FeatureCollector.Factory featureCollectors,
    Consumer<FeatureCollector.Feature> next) {
    // delegate finish handling to every layer that implements FinishHandler
    for (var handler : finishHandlers) {
      handler.finish(sourceName, featureCollectors, next);
    }
  }
Call {@code handler} for different events based on which interfaces {@code handler} implements:
{@link OsmRelationPreprocessor}, {@link FinishHandler}, {@link TilePostProcessor} or {@link LayerPostProcessor}.
planetiler-core/src/main/java/com/onthegomap/planetiler/ForwardingProfile.java