size_estimates_recorder: Increase estimate accuracy
size_estimates_recorder: Increase estimate accuracy

This patch uses the estimated_keys_for_range() function to get better
estimates.

Signed-off-by: Duarte Nunes <a60e8b7496f7715d71354fe4c06dd24017025bf1@scylladb.com>

duarten/scylla,duarten/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,duarten/scylla,scylladb/scylla,raphaelsc/scylla,raphaelsc/scylla,avikivity/scylla,avikivity/scylla,raphaelsc/scylla,scylladb/scylla