feat(ai): Implement Gemini provider with streaming and tool support

- Added GeminiLLM provider implementation with GoogleGenerativeAI SDK
- Supports streaming with text/thinking content and completion signals
- Handles Gemini's parts-based content system (text, thought, functionCall)
- Implements tool/function calling with proper format conversion
- Maps between unified types and Gemini-specific formats (model vs assistant role)
- Added test example matching other provider patterns
- Fixed typo in AssistantMessage type (stopResaon -> stopReason) across all providers

packages/ai/test/examples/gemini.ts

@@ -0,0 +1,61 @@
+import chalk from "chalk";
+import { GeminiLLM, GeminiLLMOptions } from "../../src/providers/gemini.js";
+import { Context, Tool } from "../../src/types.js";
+
+// Define a simple calculator tool
+const tools: Tool[] = [
+    {
+        name: "calculate",
+        description: "Perform a mathematical calculation",
+        parameters: {
+            type: "object" as const,
+            properties: {
+                expression: {
+                    type: "string",
+                    description: "The mathematical expression to evaluate"
+                }
+            },
+            required: ["expression"]
+        }
+    }
+];
+
+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"
+};
+
+const ai = new GeminiLLM("gemini-2.0-flash-exp", 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: [
+        {
+            role: "user",
+            content: "Think about birds briefly. Then give me a list of 10 birds. Finally, calculate 42 * 17 + 123 and 453 + 434 in parallel using the calculator tool.",
+        }
+    ],
+    tools
+}
+
+let msg = await ai.complete(context, options)
+context.messages.push(msg);
+console.log();
+console.log(chalk.yellow(JSON.stringify(msg, null, 2)));
+
+for (const toolCall of msg.toolCalls || []) {
+    if (toolCall.name === "calculate") {
+        const expression = toolCall.arguments.expression;
+        const result = eval(expression);
+        context.messages.push({
+            role: "toolResult",
+            content: `The result of ${expression} is ${result}.`,
+            toolCallId: toolCall.id,
+            isError: false
+        });
+    }
+}
+
+msg = await ai.complete(context, options);
+console.log();
+console.log(chalk.yellow(JSON.stringify(msg, null, 2)));