Add metrics for extension-rendered skill catalogs (#35597)

## What changed

- Add an optional `ExtensionMetrics` capability to thread, turn-input, and world-state contributors, backed by session telemetry in the host.
- Record skill counts, omissions, and truncated description characters for extension-rendered catalogs, tagged by the catalog surface.
- Preserve host session attribution on extension metrics, including the effective model for each turn, and prevent extension tags from overriding host metadata.
- Avoid duplicate host-catalog samples by recording world-state metrics only when the section is published or changes.

## Testing

- Cover metric values and surface tags, session metadata preservation, turn-level model changes, and host world-state publication behavior.

GitOrigin-RevId: 9059e521943a8f81df25a38b03692eddbc1d990d

codex-rs/ext/extension-api/src/lib.rs

@@ -7,6 +7,7 @@ mod user_instructions;
 pub use capabilities::AgentSpawnFuture;
 pub use capabilities::AgentSpawner;
 pub use capabilities::ExtensionEventSink;
+pub use capabilities::ExtensionMetrics;
 pub use capabilities::ExtensionWarning;
 pub use capabilities::NoopExtensionEventSink;
 pub use capabilities::NoopResponseItemInjector;