refactor(iap/apple): 优化商品ID解析逻辑以提高可读性

将原有的字符串索引查找方式改为分割字符串后遍历检查，使代码更清晰易读

internal/logic/public/iap/apple/attachTransactionLogic.go

@@ -63,32 +63,33 @@ func (l *AttachTransactionLogic) Attach(req *types.AttachAppleTransactionRequest
 	var parsedQuantity int64
 	{
 		pid := strings.ToLower(txPayload.ProductId)
-		var unitIdx = -1
-		var unitLen = 0
-		if i := strings.Index(pid, "day"); i >= 0 {
-			unitIdx, unitLen, parsedUnit = i, 3, "Day"
-		}
-		if i := strings.Index(pid, "month"); i >= 0 {
-			if unitIdx == -1 || i < unitIdx {
-				unitIdx, unitLen, parsedUnit = i, 5, "Month"
-			}
-		}
-		if i := strings.Index(pid, "year"); i >= 0 {
-			if unitIdx == -1 || i < unitIdx {
-				unitIdx, unitLen, parsedUnit = i, 4, "Year"
-			}
-		}
-		if unitIdx >= 0 {
-			sub := pid[unitIdx+unitLen:]
-			for i := 0; i < len(sub); i++ {
-				if sub[i] < '0' || sub[i] > '9' {
-					sub = sub[:i]
+		parts := strings.Split(pid, ".")
+		for i := len(parts) - 1; i >= 0; i-- {
+			p := parts[i]
+			if strings.HasPrefix(p, "day") || strings.HasPrefix(p, "month") || strings.HasPrefix(p, "year") {
+				switch {
+				case strings.HasPrefix(p, "day"):
+					parsedUnit = "Day"
+					p = p[len("day"):]
+				case strings.HasPrefix(p, "month"):
+					parsedUnit = "Month"
+					p = p[len("month"):]
+				case strings.HasPrefix(p, "year"):
+					parsedUnit = "Year"
+					p = p[len("year"):]
+				}
+				digits := p
+				for j := 0; j < len(digits); j++ {
+					if digits[j] < '0' || digits[j] > '9' {
+						digits = digits[:j]
+						break
+					}
+				}
+				if q, e := strconv.ParseInt(digits, 10, 64); e == nil && q > 0 {
+					parsedQuantity = q
 					break
 				}
 			}
-			if q, e := strconv.ParseInt(sub, 10, 64); e == nil && q > 0 {
-				parsedQuantity = q
-			}
 		}
 	}
 	l.Infow("商品映射解析", logger.Field("productId", txPayload.ProductId), logger.Field("解析单位", parsedUnit), logger.Field("解析数量", parsedQuantity))