Batch accounts when decrypting transaction notes

[dguenther]

Summary

Scanning 40+ accounts on one node right now is almost impossible due to only executing one decryptNotes batch at a time, and splitting up the decryptNotes batches per transaction and per account. In the past, this was more of a concern that the worker pool job queue would get blocked, but now that we process tasks round robin from every task queue, we should be able to keep the queue full.

With nodeWorkersMax and nodeWorkers set to 12, this increases decryption time from about 1 block per second to about 10, depending on the number of notes per block. A secondary benefit is the decryption no longer happens inside the DB lock -- the account status seems to update more frequently on this branch, but it could be due to the scan speed.

Edit: Tests pass now, this is ready for review + manual testing.

Testing Plan

• Ran a perf profile to verify that the main thread isn't blocked.

Documentation

Does this change require any updates to the Iron Fish Docs (ex. the RPC API
Reference)? If yes, link a
related documentation pull request for the website.

[ ] Yes

Breaking Change

Is this a breaking change? If yes, add notes below on why this is breaking and
what additional work is required, if any.

[ ] Yes

[hughy]

Awesome!

A couple of minor comments, but this will be a huge improvement