* Do periodic inbound compaction for rooted slots
* Add comment
* nits
* Consider not_compacted_roots in cleanup_dead_slot
* Renames in AccountsIndex
* Rename to reflect expansion of removed accounts
* Fix a comment
* rename
* Parallelize clean over AccountsIndex
* Some niceties
* Reduce locks and real chunked parallelism
* Measure each step for sampling opportunities
* Just noticed par iter is maybe lazy
* Replace storage scan with optimized index scan
* Various clean-ups
* Clear uncleared_roots even if no updates