feat(ai): Add proper thinking support for Gemini 2.5 models

- Added thinkingConfig with includeThoughts and thinkingBudget support
- Use part.thought boolean flag to detect thinking content per API docs
- Capture and preserve thought signatures for multi-turn function calling
- Added supportsThinking() check for Gemini 2.5 series models
- Updated example to demonstrate thinking configuration
- Handle SDK type limitations with proper type assertions

packages/ai/test/examples/gemini.ts

@@ -23,10 +23,15 @@ const tools: Tool[] = [
 const options: GeminiLLMOptions = {
     onText: (t, complete) => process.stdout.write(t + (complete ? "\n" : "")),
     onThinking: (t, complete) => process.stdout.write(chalk.dim(t + (complete ? "\n" : ""))),
-    toolChoice: "auto"
+    toolChoice: "auto",
+    // Enable thinking for Gemini 2.5 models
+    thinking: {
+        enabled: true,
+        budgetTokens: -1 // Dynamic thinking
+    }
 };
 
-const ai = new GeminiLLM("gemini-2.0-flash-exp", process.env.GEMINI_API_KEY || "fake-api-key-for-testing");
+const ai = new GeminiLLM("gemini-2.5-flash", process.env.GEMINI_API_KEY || "fake-api-key-for-testing");
 const context: Context = {
     systemPrompt: "You are a helpful assistant that can use tools to answer questions.",
     messages: [