message: [mempool] make mempool runtime required in LibraHandle
  Closes:
  Approved by: phoenix-antigravity
diff: @@ -39,7 +39,7 @@ const AC_SMP_CHANNEL_BUFFER_SIZE: usize = 1_024;
  pub struct LibraHandle {
  _ac: Runtime,
  - _mempool: Option<MempoolRuntime>,
  + _mempool: MempoolRuntime,
  _state_synchronizer: StateSynchronizer,
  _network_runtimes: Vec<Runtime>,
  consensus: Option<Box<dyn ConsensusProvider>>,
  @@ -252,11 +252,7 @@ pub fn setup_environment(node_config: &mut NodeConfig) -> LibraHandle {
  let admission_control_runtime = AdmissionControlService::bootstrap(&node_config, ac_sender);
  instant = Instant::now();
  - let mempool = Some(MempoolRuntime::bootstrap(
  - node_config,
  - mempool_network_handles,
  - client_events,
  - ));
  + let mempool = MempoolRuntime::bootstrap(node_config, mempool_network_handles, client_events);
  debug!("Mempool started in {} ms", instant.elapsed().as_millis());
  let mut consensus = None;
  if let Some((peer_id, runtime, mut network_provider)) = validator_network_provider {
  