[MCP] Add auth status to MCP servers (#4918)

This adds a queryable auth status for MCP servers which is useful:
1. To determine whether a streamable HTTP server supports auth or not
based on whether or not it supports RFC 8414-3.2
2. Allow us to build a better user experience on top of MCP status

codex-rs/core/src/lib.rs

@@ -32,6 +32,7 @@ pub mod executor;
 mod flags;
 pub mod git_info;
 pub mod landlock;
+pub mod mcp;
 mod mcp_connection_manager;
 mod mcp_tool_call;
 mod message_history;