Add GoogleAITokenCounter

Author: intitni

Tool/Sources/TokenEncoder/GoogleAITokenCounter.swift

@@ -0,0 +1,13 @@
+import GoogleGenerativeAI
+
+public final class GoogleAITokenCounter: TokenCounter {
+    let model: GenerativeModel
+    
+    public init(model: GenerativeModel) {
+        self.model = model
+    }
+    
+    public func countToken(text: String) async -> Int {
+        (try? await model.countTokens(text))?.totalTokens ?? text.count
+    }
+}