feat(sale): 添加总成本字段

- 在 Benefit 结构中添加 TotalCost 字段，用于计算总成本
- 该字段的添加有助于更全面地分析销售数据和利润情况

erp/sale/benefit.go

@@ -71,6 +71,7 @@ type ReplyBenefitInfo struct {
 	ForeignSafeCost       decimal.Decimal `json:"foreignSafeCost"`
 	ForeignCommission     decimal.Decimal `json:"foreignCommission"`
 	Expense               decimal.Decimal `json:"expense"`
+	TotalCost             decimal.Decimal `json:"totalCost"`
 	Income                decimal.Decimal `json:"income"`
 	IncomePurchase        decimal.Decimal `json:"incomePurchase"`
 	ProfitAndLoss         decimal.Decimal `json:"profitAndLoss"`