This PR adds performance improvements to the sentinel attestations:
Validation and attestation happen in parallel threads in the sentinel
Attestation requests are prioritized by sentinels such that the end-to-end latency of transactions reduces under high(er) load: incoming transactions will wait until existing transactions pending attestation are completed.
Validation of attestations happens in parallel in the coordinator
Validation of attestations happens in parallel and outside of the state machine (before replication) in the shard.
This PR adds performance improvements to the sentinel attestations: