In general aim for the happy case when the exposer lists the buckets
in ascending order.
Use Compact(2) to compact the result of nhcb convert.
This is more in line with how client_golang optimizes spans vs
buckets.
aef8aedb4b/prometheus/histogram.go (L1485)
Signed-off-by: György Krajcsovits <gyorgy.krajcsovits@grafana.com>