Function handle_receive_proposal

async fn handle_receive_proposal(
    handler: ProtocolGenericHandlerPtr<ProposalMessage, ProposalMessage>,
    tasks: Arc<RwLock<HashSet<StoppableTaskPtr>>>,
    validator: ValidatorPtr,
    p2p: P2pPtr,
    proposals_sub: JsonSubscriber,
    blocks_sub: JsonSubscriber,
    executor: ExecutorPtr,
) -> Result<()>

Background handler function for ProtocolProposal.