RocksDB has added version 3 and version 4 sstable formats:

• Version 3 changes index block keys to not include the sequence number (which is always 0?)
• Version 4 changes index block values (block handles) from being encoded as <offset, size> to a delta encoding that usually only stores <size>.

There is no particular urgency to supporting these formats, but we should investigate whether these format changes move the needle on any benchmarks.

Jira issue: PEBBLE-185