Interrupt and drain canceled classifier responses before socket reuse (#53698)

## Why

Canceled classifier requests need bounded cleanup that preserves received token usage and returns only safe WebSocket connections to the pool.

## What changed

- Own classifier response streams and connection leases together, interrupting dropped responses with a one-second cleanup deadline.
- Require a matching interruption acknowledgement and response completion before reusing a canceled response's socket. Retire sockets on rejection, invalid acknowledgements, or timeout while preserving any received completion and token usage.
- Skip requests canceled before dispatch and return their unused sockets to the pool.
- Distinguish cancellation from ordinary steering, which continues draining without requiring an interruption acknowledgement.

## Testing

Add regression coverage for cancellation, acknowledgement ordering and failures, cleanup timeouts, socket reuse, and token accounting under backpressure. Extend steering tests to cover rejected and missing acknowledgements.

GitOrigin-RevId: c4e7aac49d36cea2c2d0e9f2ba5f6147f67471dd

codex-rs/core/src/session/turn.rs

@@ -2689,7 +2689,7 @@ async fn try_run_sampling_request(
             Ok(Err(_)) => {
                 if let Some(interrupt) = stream.interrupt.take() {
                     if step_context.settings.model_info.use_responses_lite {
-                        let _ = interrupt.send(());
+                        let _ = interrupt.send(codex_api::ResponseInterrupt::Drain);
                     }
                     // Drain the response normally before reusing its connection and history.
                     preempt = CancellationToken::new();