Respect model support for reasoning summaries (#32290)

## What changed

- Add `supports_reasoning_summary_parameter` to model metadata, defaulting to
  `true` for backward compatibility.
- Omit `reasoning.summary` and its summary-delivery stream option when the
  selected model does not support the parameter.
- Apply the capability of the final selected model when a spawned agent uses a
  different model.

## Testing

- Cover unsupported models in regular requests and spawned-agent model
  overrides.

GitOrigin-RevId: 72b783799fc0685cef1501ef2dbf62d1308ceead

codex-rs/codex-api/tests/models_integration.rs

@@ -81,6 +81,7 @@ async fn models_client_hits_models_endpoint() {
             base_instructions: "base instructions".to_string(),
             model_messages: None,
             include_skills_usage_instructions: false,
+            supports_reasoning_summary_parameter: true,
             default_reasoning_summary: ReasoningSummary::Auto,
             support_verbosity: false,
             default_verbosity: None,