[Prover][Test] Broker failure: system must recover if the `ProvingBroker` goes down

[alexghr]

Scenario:

1. start proving a block
2. accumulate some in proving jobs
3. shut down ProvingBroker
4. wait 5 minutes
5. start ProvingBroker

Expected:

• orchestrator retries requests to ProvingBroker until it recovers
• agents retry requests to ProvingBroker until it recovers
• agents do not lose finished proofs that didn't get posted back to the broker
• after ProvingBroker re-initializes block proving continue from where it left off