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