Missing sync logic for "richlist" and "blockstats"

Working with `tools/sync.js` and `tools/richlist.js`, there are some issues that need to be addressed.

- [ ] Ignore / Remove 0 balance accounts while on sync.
- [ ] Trigger full sync mode for "blockstats" and "richlist" without syncing them with blocks. ( This requires to remove logic for RESCAN and integrate them on single "sync.js" file.

Calling original author @hackmod for help.

Start by reading tools/sync.js and tools/richlist.js, then trace the existing RESCAN handling for blockstats and richlist. Done means zero-balance accounts are ignored during sync, and blockstats and richlist can run in full-sync mode without syncing alongside blocks, with the logic integrated into sync.js.

Written by the indexing model from the issue text.