Adding an array multiple times leads to the fast update via `IncRC`.
This hides the allocation that is there on the first addition. In this
commit add another benchmark which measures Add/Remove together, to
ensure that `switch` in `refCounter.Add` is entered. Benchmark results
are meaningful, because `Add`/`Remove` have almost identical implementation.
Signed-off-by: Evgeniy Stratonikov <evgeniy@nspcc.ru>
