qa: verify the benefits of mempool cacheline optimization

qa: verify the benefits of mempool cacheline optimization

There already is a test to verify the mempool sharding works, in the sense that
it uses at least half of the variables available to count the number of
allocated objects and their total size. This new test verifies that, with
sharding, object counting is at least twice faster than without sharding. It
also collects cacheline contention data with the perf c2c tool. The manual
analysis of this data shows the optimization gain is indeed related to cacheline
contention.

Fixes: https://tracker.ceph.com/issues/49896
Signed-off-by: Loïc Dachary <loic@dachary.org>