public Map<String, Object> getAttrsAtZoom(int zoom) {
      if (!mustUnwrapValues) {
        return attrs;
      }
      if (attrCache == null) {
        attrCache = CacheByZoom.create(this::computeAttrsAtZoom);
      }
      return attrCache.get(zoom);
    }
Returns the attribute to put on all output vector tile features at a zoom level.
planetiler-core/src/main/java/com/onthegomap/planetiler/FeatureCollector.java