tests/imr: add test for optional<T>
tests/imr: add test for optional<T>

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