Added MCP server command to enable authentication using ChatGPT (#2373)

This PR adds two new APIs for the MCP server: 1) loginChatGpt, and 2)
cancelLoginChatGpt. The first starts a login server and returns a local
URL that allows for browser-based authentication, and the second
provides a way to cancel the login attempt. If the login attempt
succeeds, a notification (in the form of an event) is sent to a
subscriber.

I also added a timeout mechanism for the existing login server. The
loginChatGpt code path uses a 10-minute timeout by default, so if the
user fails to complete the login flow in that timeframe, the login
server automatically shuts down. I tested the timeout code by manually
setting the timeout to a much lower number and confirming that it works
as expected when used e2e.

codex-rs/login/src/lib.rs

@@ -18,6 +18,7 @@ use std::time::Duration;
 
 pub use crate::server::LoginServer;
 pub use crate::server::ServerOptions;
+pub use crate::server::ShutdownHandle;
 pub use crate::server::run_login_server;
 pub use crate::token_data::TokenData;
 use crate::token_data::parse_id_token;