add token count for Gemini models

Hello, thanks for creating this! It looks super interesting. With Gemini having 1 million tokens available. And the possibility to get 2 million soon, it will be amazing to see the amount of tokens for them. https://ai.google.dev/gemini-api/docs/get-started/tutorial?lang=web#count-tokens

Thanks in advance for considering! Greetings from Franconia (Germany)