Error out if chain listener fails to start in benchmark client (#4449)

## Motivation

Currently if the chain listener fails to start, we just continue with
the benchmarks. However, if we want to ensure they're more "realistic",
we should enforce that the chain listener is properly running.

## Proposal

Error out if the chain listener fails to start

## Test Plan

Benchmark a network using this.

## Release Plan

- Nothing to do / These changes follow the usual release cycle.

Author: ndr-ds

linera-client/src/benchmark.rs

@@ -75,6 +75,8 @@ pub enum BenchmarkError {
     NotEnoughChainsInWallet(usize, usize),
     #[error("Random number generator error: {0}")]
     RandError(#[from] rand::Error),
+    #[error("Chain listener startup error")]
+    ChainListenerStartupError,
 }
 
 #[derive(Debug)]
@@ -130,10 +132,11 @@ impl<Env: Environment> Benchmark<Env> {
         let notifier = Arc::new(Notify::new());
         let barrier = Arc::new(Barrier::new(num_chains + 1));
 
-        let chain_listener_result = chain_listener.run().await;
-
-        let chain_listener_handle =
-            tokio::spawn(async move { chain_listener_result?.await }.in_current_span());
+        let chain_listener_future = chain_listener
+            .run()
+            .await
+            .map_err(|_| BenchmarkError::ChainListenerStartupError)?;
+        let chain_listener_handle = tokio::spawn(chain_listener_future.in_current_span());
 
         let bps_control_task = Self::bps_control_task(
             &barrier,