Function start_oauth_callback_server_random_port 

pub fn start_oauth_callback_server_random_port() -> Result<(OAuthCallbackServer, String)>

Start a local TCP listener on a random available port and return both the callback server and the http://localhost:{port}/callback redirect URI.

This is useful for OAuth providers (like GitHub Copilot and GitLab) that accept localhost redirect URIs but don’t have a fixed port pre-registered. The caller should include the returned redirect_uri in the authorization URL query parameters.