Compactor needs to be implemented. See details in parent and blocking jira.
create integration/perf tests for stripe compactions
record on-disk data size for store file and make it available during writing
implement compaction policy for stripe compactions
refactor default compactor to make its parts easier to reuse
allow StoreScanner to drop deletes from some part of the compaction range
expose the number of seen KVs from StoreScanner