@Override
    public List<MetricFamilySamples> collect() {
      List<Collector.MetricFamilySamples> results = new ArrayList<>();
      for (var entry : heapObjectsToMonitor.entrySet()) {
        String name = sanitizeMetricName(entry.getKey());
        MemoryEstimator.HasEstimate heapObject = entry.getValue();
        results
          .add(new GaugeMetricFamily(BASE + "heap_object_" + name + "_size_bytes", "Bytes of memory used by " + name,
            heapObject.estimateMemoryUsageBytes()));
      }
      return results;
    }
Reports stats on all in-memory objects sizes being monitored through
{@link #monitorInMemoryObject(String, MemoryEstimator.HasEstimate)}.
planetiler-core/src/main/java/com/onthegomap/planetiler/stats/PrometheusStats.java