mergeSumDouble
Merge a remote GCounterDouble snapshot into this exporter's double-sum for key.
Idempotent: merging the same snapshot twice produces the same result. Returns MetricExportResult.Success after the durable write.
Merge a remote GCounterDouble snapshot into this exporter's double-sum for key.
Idempotent: merging the same snapshot twice produces the same result. Returns MetricExportResult.Success after the durable write.