✨ Added support for response formats

[jeffreyvr]

Added the option to set a response format including a test.

The Grok API supports setting a response format, also refered to structured outputs, for the grok-2-1212 model.

$options = new ChatOptions(model: Model::GROK_2_1212, temperature: 0.7, stream: false, responseFormat: ['type' => 'json_object']);
$response = $client->chat($messages, $options);

[thefeqy]

Thanks for your contribution. I just need to test it and merge it right away.

[thefeqy]

Great job on this!

Just a small issue—our tests no longer interact with the actual Grok API. Instead, we now use fake responses, which is causing the tests you've written to fail.

There's also a minor conflict with the README.md file.

Thanks for your contribution! Looking forward to merging this PR soon. 🚀

[jeffreyvr]

Thanks! Conflicts have been resolved. Made a minor change to the mock response to allow for setting specific data to be returned.