- Use a bitset to track used buckets in the `SharedArenaHashmap`, allowing for more efficient iteration
- Create a global pool for both `MemoryArena` and `IndexingContext`
- Reduce the MemoryArea page size by half (it's now 512KB instead of 1MB)
- Centralize thread pool instances in `SegmentUpdater` so we can elide making them if all nthread sizes are zero