mvcc: Improve printout of partition_snapshot_row_cursor
mvcc: Improve printout of partition_snapshot_row_cursor

Multiline output is easier to read by humans.
Also, print continuity.

Message-Id: <5f2f19480942d236d0e8e619bd9101e1c9d4f4ec@scylladb.com>

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