pub fn new() -> Self {
        Self {
            model: QwenModel::QwenTurbo.to_string(), // Default to Turbo model
            options: CallOptions::default(),
            api_key: std::env::var("QWEN_API_KEY").unwrap_or_default(),
            base_url: "https://dashscope.aliyuncs.com/compatible-mode/v1/chat/completions"
                .to_string(),
        }
    }
Create a new Qwen client with default settings
src/llm/qwen/client.rs