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/client_common.rs

@@ -117,7 +117,7 @@ fn normalize_image_detail(detail: &mut Option<ImageDetail>, model_info: &ModelIn
 
 pub struct ResponseStream {
     pub(crate) rx_event: mpsc::Receiver<Result<ResponseEvent>>,
-    pub(crate) interrupt: Option<oneshot::Sender<()>>,
+    pub(crate) interrupt: Option<oneshot::Sender<codex_api::ResponseInterrupt>>,
     /// Signals the mapper task that the consumer stopped polling before the
     /// provider stream reached its own terminal event.
     pub(crate) consumer_dropped: CancellationToken,