Pre-initialize global rayon threadpool (#41226)

We only use it a handful of times and the default amount of threads
(logical cpu core number) its spawns is overkill for this. This also
gives the threads names oppose to being labeled `<unknown>`

Release Notes:

- N/A *or* Added/Fixed/Improved ...

crates/remote_server/src/unix.rs

@@ -370,6 +370,12 @@ pub fn execute_run(
 
     let listeners = ServerListeners::new(stdin_socket, stdout_socket, stderr_socket)?;
 
+    rayon::ThreadPoolBuilder::new()
+        .num_threads(4)
+        .thread_name(|ix| format!("RayonWorker{}", ix))
+        .build_global()
+        .unwrap();
+
     let (shell_env_loaded_tx, shell_env_loaded_rx) = oneshot::channel();
     app.background_executor()
         .spawn(async {