fix: Do not access attestation pool in prover p2p client

We dont spin up an attestation pool in prover p2p clients, since we dont
care to track them. We only subscribe to the topic so we can know which
txs may be interesting later and mark them as non-evictable.

Author: spalladino

yarn-project/p2p/src/services/libp2p/libp2p_service.ts

@@ -810,7 +810,10 @@ export class LibP2PService<T extends P2PClientType = P2PClientType.Full> extends
     const validationFunc: () => Promise<ReceivedMessageValidationResult<BlockProposal>> = async () => {
       const block = BlockProposal.fromBuffer(payloadData);
       const isValid = await this.validateBlockProposal(source, block);
-      const exists = isValid && (await this.mempools.attestationPool!.hasBlockProposal(block));
+
+      // Note that we dont have an attestation pool if we're a prover node, but we still
+      // subscribe to block proposal topics in order to prevent their txs from being cleared.
+      const exists = isValid && (await this.mempools.attestationPool?.hasBlockProposal(block));
 
       this.logger.trace(`Validate propagated block proposal`, {
         isValid,