feat(支付): 添加支付金额转换日志并优化代码结构

为支付宝、Stripe、Epay和CryptoSaaS支付逻辑添加金额转换的日志记录
将支付请求参数提取为变量并添加日志记录
优化代码结构，提高可读性和可维护性

scripts/rounding-demo/main.go

@@ -0,0 +1,25 @@
+package main
+
+import (
+    "fmt"
+    "math"
+)
+
+func main() {
+    price := int64(300 * 7)
+    discountPercent := 95.19
+    discount := discountPercent / 100.0
+    amount := int64(math.Round(float64(price) * discount))
+    fmt.Printf("price_cents=%d discount=%.4f amount_cents=%d amount=%.2f\n", price, discount, amount, float64(amount)/100.0)
+
+    couponPercent := 10.0
+    coupon := int64(math.Round(float64(amount) * (couponPercent / 100.0)))
+    amount -= coupon
+    fmt.Printf("coupon_percent=%.2f coupon_cents=%d amount_cents=%d amount=%.2f\n", couponPercent, coupon, amount, float64(amount)/100.0)
+
+    feePercent := 5.0
+    fee := int64(math.Round(float64(amount) * (feePercent / 100.0)))
+    total := amount + fee
+    fmt.Printf("fee_percent=%.2f fee_cents=%d total_cents=%d total=%.2f\n", feePercent, fee, total, float64(total)/100.0)
+}
+