Function place_order_with_options_and_identity 

pub async fn place_order_with_options_and_identity(
    client: &FutuClient,
    params: &PlaceOrderParams,
    options: &PlaceOrderOptions,
) -> Result<PlaceOrderResultWithIdentity>

下单（带官方 FTAPI optional 字段）并返回 numeric/string 双订单身份。