chore: import upstream snapshot with attribution

examples/eval-function-tools-callback/README.md

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+# eval-function-tools-callback (Function Tool Callbacks Example)
+
+You can run this example with:
+
+```bash
+npx promptfoo@latest init --example eval-function-tools-callback
+cd eval-function-tools-callback
+```
+
+This example demonstrates how to use promptfoo to evaluate OpenAI's function calling capabilities with the gpt-4o, utilizing the `functionToolCallbacks` feature.
+
+## Configuration
+
+See `promptfooconfig.js` for the full configuration, including prompts, provider setup, and test cases.
+
+## Running the Example
+
+```bash
+promptfoo eval -c [path to examples/eval-function-tools-callback/]promptfooconfig.js
+```
+
+For more details on function calling and OpenAI tools, refer to:
+
+- [OpenAI Function Calling Guide](https://platform.openai.com/docs/guides/function-calling)
+- [Promptfoo OpenAI Provider Documentation](https://promptfoo.dev/docs/providers/openai)

examples/eval-function-tools-callback/promptfooconfig.js

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+module.exports = /** @type {import('promptfoo').TestSuiteConfig} */ ({
+  prompts: [
+    'Please add the following numbers together: {{a}} and {{b}}',
+    'What is the sum of {{a}} and {{b}}?',
+  ],
+  providers: [
+    {
+      id: 'openai:gpt-4.1-mini',
+      config: {
+        model: 'gpt-4.1-mini',
+        temperature: 0,
+        tools: [
+          {
+            type: 'function',
+            function: {
+              name: 'addNumbers',
+              description: 'Add two numbers together',
+              parameters: {
+                type: 'object',
+                properties: {
+                  a: { type: 'number' },
+                  b: { type: 'number' },
+                },
+                required: ['a', 'b'],
+              },
+            },
+          },
+        ],
+        tool_choice: 'auto',
+        functionToolCallbacks: {
+          addNumbers: (parametersJsonString) => {
+            const { a, b } = JSON.parse(parametersJsonString);
+            return JSON.stringify(a + b);
+          },
+        },
+      },
+    },
+  ],
+  tests: [
+    {
+      vars: { a: 5, b: 6 },
+      assert: [
+        {
+          type: 'equals',
+          value: '11',
+        },
+      ],
+    },
+    {
+      vars: { a: 10, b: 20 },
+      assert: [
+        {
+          type: 'javascript',
+          value: "output.includes('30')",
+        },
+      ],
+    },
+  ],
+});