docs: def add_stock(self, product_id, sku_info, quantity):
          """
          增加库存
  
          :param product_id: 商品ID
          :param sku_info: sku信息,格式"id1:vid1;id2:vid2",如商品为统一规格，则此处赋值为空字符串即可
          :param quantity: 增加的库存数量
          :return: 返回的 JSON 数据包
          """
          return self._post(
              'merchant/stock/add',
              data={
                  "product_id": product_id,
                  "sku_info": sku_info,
                  "quantity": quantity
              }
          )