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/codex-api/src/lib.rs

@@ -40,6 +40,7 @@ pub use crate::common::ReasoningSummaryDelivery;
 pub use crate::common::ResponseCreateWsRequest;
 pub use crate::common::ResponseEvent;
 pub use crate::common::ResponseId;
+pub use crate::common::ResponseInterrupt;
 pub use crate::common::ResponseStream;
 pub use crate::common::ResponsesApiRequest;
 pub use crate::common::ResponsesApiTools;