Specify API format in SDK

What feature would you like to see?

In the SDK, as far as I know, there's no way to specify using the chat completions API. This is useful for AI Gateways that are not compatible with the Responses API.

Additional information

Would love to be able to configure:

const codex = new Codex({
    baseUrl: "https://example.gateway.com/v1",
    apiKey: process.env.GATEWAY_API_KEY,
    wireApi: "chat"
  });