docs: @SuppressWarnings("rawtypes")
      public Gauge gauge(String name, final MetricSupplier<Gauge> supplier) {
          return getOrAdd(name, new MetricBuilder<Gauge>() {
              @Override
              public Gauge newMetric() {
                  return supplier.newMetric();
              }
  
              @Override
              public boolean isInstance(Metric metric) {
                  return Gauge.class.isInstance(metric);
              }
          });
      }