Add a dual-WebSocket transport for code mode (#36812)

## Why

Large nested-tool callbacks can occupy a WebSocket and delay unrelated session
operations on the same code-mode connection.

## What changed

- Negotiate the optional `dual-websocket-v1` capability and pair a second,
  token-scoped WebSocket with the control connection.
- Route nested-tool callbacks and their results over the bulk socket while
  keeping session operations, notifications, and execution responses on the
  control socket. Reject messages sent on the wrong lane.
- Preserve the single-connection transport when the capability is unavailable,
  and bound pairing, queued callbacks, and deferred cross-socket messages.
- Defer callbacks that arrive before their execution-started response, and
  return delegate errors without disconnecting the connection.

## Testing

Add protocol, transport, driver, and WebSocket integration coverage for
capability negotiation, lane routing, pairing failures, out-of-order messages,
and progress during large concurrent tool results.

GitOrigin-RevId: fa4504653e7cbf3c4ec930ae57aa0a41345bad66

codex-rs/Cargo.lock

@@ -2571,6 +2571,7 @@ dependencies = [
  "tokio-util",
  "tracing",
  "tracing-subscriber",
+ "uuid",
 ]
 
 [[package]]