Omit undersized WAV output from Code Mode (#41934)

## Why

Audio models cannot reliably encode tool-generated clips shorter than 25 ms.

## What changed

- Measure the available audio frames in base64-encoded PCM and IEEE float WAV outputs.
- Replace clips under 25 ms with explanatory text while preserving surrounding Code Mode output.
- Leave clips at or above the threshold and unrecognized audio formats unchanged.

## Testing

- Cover the duration boundary across multiple sample rates and all supported `audio()` input forms.
- Verify bounded and truncated WAV chunks, output after `yield_control()`, and end-to-end mixed text and audio output.

GitOrigin-RevId: 342b4bdbc65db4238580f9cdc372763c2576eca5

codex-rs/code-mode-runtime/src/service_tests.rs

@@ -1189,6 +1189,9 @@ audio({
     );
 }
 
+#[path = "service_audio_tests.rs"]
+mod audio_tests;
+
 #[tokio::test]
 async fn audio_helper_rejects_non_data_urls() {
     for source in [