@Override
  public void processFeature(SourceFeature sourceFeature, FeatureCollector features) {
    // delegate source feature processing to each handler for that source
    for (var handler : getHandlerIndex().getMatches(sourceFeature)) {
      handler.processFeature(sourceFeature, features);
    }
  }
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