Google Gemini adapter

import { GoogleGenerativeAI } from "@google/generative-ai";
import { meter } from "llmmeter-google";

const genAI = new GoogleGenerativeAI(process.env.GOOGLE_API_KEY!);
const model = meter(genAI.getGenerativeModel({ model: "gemini-1.5-pro" }));

const r = await model.generateContent("Hello");
const stream = await model.generateContentStream("Tell me a story");

Wraps generateContent, generateContentStream, embedContent, and batchEmbedContents. Reads usageMetadata for promptTokenCount, candidatesTokenCount, cachedContentTokenCount, and thoughtsTokenCount (reasoning).