Add a route-aware HTTP client pool (#34447)

## Why

PAC and system-proxy resolution can select a different outbound route for each
request URL. Request creation and route selection must use the same URL while
still allowing transport clients to be reused.

## What changed

- Add `RouteAwareClientPool` and a request builder that resolve the outbound
  proxy route when sending each request.
- Reuse HTTP clients by resolved route, with a bounded cache of 16 routes.
- Preserve request tracing, optional diagnostic logging, custom CA settings,
  Cloudflare cookies, and default transport redirect behavior.
- Export route-aware response and error types, including status, timeout, and
  connection-error helpers.

## Testing

Add tests for exact URL routing, client reuse and eviction, default redirects,
and redaction of URL secrets from debug output.

GitOrigin-RevId: a1688b64305a0bb276c371df63a039ccbe821b76

codex-rs/http-client/src/lib.rs

@@ -5,6 +5,7 @@ mod default_client;
 mod error;
 mod outbound_proxy;
 mod request;
+mod route_aware_client_pool;
 mod transport;
 
 pub use crate::chatgpt_cloudflare_cookies::with_chatgpt_cloudflare_cookie_store;
@@ -21,6 +22,8 @@ pub use crate::custom_ca::build_reqwest_client_with_custom_ca;
 pub use crate::custom_ca::build_rustls_client_config_with_custom_ca;
 pub use crate::custom_ca::maybe_build_rustls_client_config_with_custom_ca;
 pub use crate::default_client::HttpClient;
+pub use crate::default_client::HttpError;
+pub use crate::default_client::HttpResponse;
 pub use crate::default_client::RequestBuilder;
 pub use crate::error::StreamError;
 pub use crate::error::TransportError;
@@ -36,6 +39,10 @@ pub use crate::request::Request;
 pub use crate::request::RequestBody;
 pub use crate::request::RequestCompression;
 pub use crate::request::Response;
+pub use crate::route_aware_client_pool::RouteAwareClientPool;
+pub use crate::route_aware_client_pool::RouteAwareClientPoolError;
+pub use crate::route_aware_client_pool::RouteAwareRequestBuilder;
+pub use crate::route_aware_client_pool::RouteAwareRequestError;
 pub use crate::transport::ByteStream;
 pub use crate::transport::HttpTransport;
 pub use crate::transport::ReqwestTransport;