tests: sstables: Check that reading large index pages does not cause large allocations
tests: sstables: Check that reading large index pages does not cause large allocations

Reproducer of #3597.

Message-Id: <6813a3480eda76bb64c51028e83389352663d8ae@scylladb.com>

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