Function createExtensionRunner

createExtensionRunner(webviewPanel: WebviewPanel): Promise<Runner>
Creates a Runner instance for extension-side tool execution

The Runner uses a smart executor that:
- Executes VS Code-specific operations locally (they need VS Code APIs)
- Bridges notebook/lexical operations to webview (they need document state)
Parameters
- webviewPanel: WebviewPanel
  VS Code webview panel for message communication
Returns Promise<Runner>
Promise resolving to Runner instance configured with smart executor
Example
```
const runner = await createExtensionRunner(webviewPanel);
const result = await runner.execute("insertCell", {
  cellType: "code",
  source: "print('hello')"
});
```
- Defined in src/tools/core/runnerSetup.ts:130