* Initialize the rayon threadpool with a new config for CPU-bound threads
* Verify proofs and signatures on the rayon thread pool
* Only spawn one concurrent batch per verifier, for now
* Allow tower-batch to queue multiple batches
* Fix up a potentially incorrect comment
* Rename some variables for concurrent batches
* Spawn multiple batches concurrently, without any limits
* Simplify batch worker loop using OptionFuture
* Clear pending batches once they finish
* Stop accepting new items when we're at the concurrent batch limit
* Fail queued requests on drop
* Move pending_items and the batch timer into the worker struct
* Add worker fields to batch trace logs
* Run docker tests on PR series
* During full verification, process 20 blocks concurrently
* Remove an outdated comment about yielding to other tasks
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