perf-test : Print B-tree sizes
perf-test : Print B-tree sizes

After the switch from BST to B-tree the memory foorprint includes inner/leaf nodes
from the B-tree, so it's useful to know their sizes too.

Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@scylladb.com>

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla