Base2 Exponential Histogram Aggregation Performance

[ethandmd]

Follow up from PR #3346 review comment

1. Base2 Exponential Histogram Aggregation downscaling in-place.
2. Aggregation benchmarks for throughput when multiple threads are involved.

Something along the lines of what’s done in measurements_benchmark.cc

[github-actions]

This issue was marked as stale due to lack of activity.