test/boost/mutation_reader_test: multishard reader: add tests for fast-forwarding with read-ahead
test/boost/mutation_reader_test: multishard reader: add tests for fast-forwarding with read-ahead

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