refactor: describe the FIFO loop exit condition

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: lvaroqui

src/executor/shared/fifo.rs

@@ -180,7 +180,7 @@ impl RunnerFifo {
 
         let mut benchmark_started = false;
 
-        // Inner loop: process commands until timeout/error
+        // Process commands until the child process exits
         loop {
             tokio::select! {
                 result = self.recv_cmd() => {