PersistedCompactionMap could release reference to records early

Whenever a PersistedCompactionMap becomes empty it will be eventually dropped from the compaction maps chain. this will happen on the next compaction cycle, which happens post-cleanup. so we're potentially keeping a reference to some collectable garbage for up to 2 cycles.
I'd like to propose a patch that allows for eagerly nullifying the reference to the records, making this interval shorter.