Add worker_threads support to backfilling

[ashayp22]

Bun v1.1.13 added more support for worker_threads, which should now let us use worker_threads for parallelizing the unstake event backfilling.

Update

• Retried with Bun v1.1.19, and now facing this error. The error is still being resolved in this PR.

TODO

• [ ] Replace Promise.all with thread.js Thread Pool in createBackfiller.ts
• [ ] Benchmark performance in threading vs promises

[ashayp22]

11 sped up backfilling with async/await. Threads will be helpful for computationally intense indexing, but no such indexers exist as of right now (both unstake-indexer and quark-indexer are I/O intensive). We should look into this enhancement based on if computationally intense indexers are created.