Add websocket telemetry metrics and labels (#10316)

Summary
- expose websocket telemetry hooks through the responses client so
request durations and event processing can be reported
- record websocket request/event metrics and emit runtime telemetry
events that the history UI now surfaces
- improve tests to cover websocket telemetry reporting and guard runtime
summary updates


<img width="824" height="79" alt="Screenshot 2026-01-31 at 5 28 12 PM"
src="https://github.com/user-attachments/assets/ea9a7965-d8b4-4e3c-a984-ef4fdc44c81d"
/>

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

@@ -40,3 +40,4 @@ pub use crate::requests::ResponsesRequest;
 pub use crate::requests::ResponsesRequestBuilder;
 pub use crate::sse::stream_from_fixture;
 pub use crate::telemetry::SseTelemetry;
+pub use crate::telemetry::WebsocketTelemetry;