Add spacing to timer duration formats (#3471)

<img width="426" height="28" alt="image"
src="https://github.com/user-attachments/assets/b281aca3-3c8d-4b88-a017-5d2f8ea9f3d5"
/>

codex-rs/common/src/elapsed.rs

@@ -69,4 +69,10 @@ mod tests {
         let dur_long = Duration::from_millis(3_601_000);
         assert_eq!(format_duration(dur_long), "60m 01s");
     }
+
+    #[test]
+    fn test_format_duration_one_hour_has_space() {
+        let dur_hour = Duration::from_millis(3_600_000);
+        assert_eq!(format_duration(dur_hour), "60m 00s");
+    }
 }