Upsert by version

Implement an upsert/merge that collapses a change stream into the latest state per key. Given a list of change records [key, version, value] (key string, version int, value string), produce the final table keeping, for each key, the record with the HIGHEST version. If two records share a key and the same highest version, keep the one that appears LATER in the input list (last-write-wins tie-break). Return [key, version, value] rows sorted by key ascending. Up to 50000 records.