default void finish(String sourceName, FeatureCollector.Factory featureCollectors,
    Consumer<FeatureCollector.Feature> next) {}
Invoked once for each source after all elements for that source have been processed.

@param sourceName        the name of the source that just finished
@param featureCollectors a supplier for new {@link FeatureCollector} instances for a {@link SourceFeature}.
@param next              a consumer to pass finished map features to
planetiler-core/src/main/java/com/onthegomap/planetiler/Profile.java