fix(价格展示): 修复模板渲染时极小价格被折叠为 0.00 的问题

Motivation:
此前的修复仅覆盖直接拼接文案的场景，跟单等基于模板渲染的推送场景中，%.2f 格式化仍会把 PEPE 等 Meme 币的极小价格（如 0.00000059）折叠为 0.00，导致交易通知丢失真实价格、误导用户。

Changes:

* 抽取共享的价格显示逻辑到统一显示层，两个订阅者改为复用，移除重复实现
* 新增 Decimal 类型，渲染时以副本方式包装模板数据，使模板内 printf 风格格式化保留极小价格精度且不出现科学计数法，同时不修改调用方原始数据
* 渲染引擎空值判断改用反射实现，覆盖全部整型、无符号整型与浮点类型
* 补充转换到渲染的端到端回归测试，覆盖极小价格精度、科学计数法与数据不可变性

internal/subscriber/tradesignal/format.go

@@ -2,10 +2,9 @@ package tradesignal
 
 import (
 	"fmt"
-	"math"
-	"strconv"
 	"strings"
 
+	"aiaa-notification-service/internal/display"
 	"aiaa-notification-service/internal/tz"
 )
 
@@ -31,7 +30,7 @@ func Format(signal *Signal, opts ...FormatOptions) string {
 	action := strings.ToUpper(signal.Action)
 	switch action {
 	case "OPEN":
-		lines = append(lines, fmt.Sprintf("开仓价格: %s", formatPrice(signal.Price)))
+		lines = append(lines, fmt.Sprintf("开仓价格: %s", display.FormatPrice(signal.Price)))
 		if line := sizeLine("OPEN", signal.Quantity, signal.AmountMarginRatio); line != "" {
 			lines = append(lines, line)
 		}
@@ -40,23 +39,23 @@ func Format(signal *Signal, opts ...FormatOptions) string {
 			lines = append(lines, fmt.Sprintf("杠杆: %dx", signal.Leverage))
 		}
 		if signal.TakeProfitPrice != nil {
-			lines = append(lines, fmt.Sprintf("止盈价格: %s", formatPrice(*signal.TakeProfitPrice)))
+			lines = append(lines, fmt.Sprintf("止盈价格: %s", display.FormatPrice(*signal.TakeProfitPrice)))
 		}
 		if signal.StopLossPrice != nil {
-			lines = append(lines, fmt.Sprintf("止损价格: %s", formatPrice(*signal.StopLossPrice)))
+			lines = append(lines, fmt.Sprintf("止损价格: %s", display.FormatPrice(*signal.StopLossPrice)))
 		}
 	case "CLOSE":
-		lines = append(lines, fmt.Sprintf("平仓价格: %s", formatPrice(signal.Price)))
+		lines = append(lines, fmt.Sprintf("平仓价格: %s", display.FormatPrice(signal.Price)))
 		lines = append(lines, closeSizeLine(signal.Quantity, signal.PosMarginRatio))
 		lines = appendAvgPrice(lines, opt.AvgPrice)
 		if signal.PnL != nil {
-			lines = append(lines, fmt.Sprintf("平仓盈亏: %s", formatPrice(*signal.PnL)))
+			lines = append(lines, fmt.Sprintf("平仓盈亏: %s", display.FormatPrice(*signal.PnL)))
 		}
 		if signal.AccountBalance != nil {
-			lines = append(lines, fmt.Sprintf("账户余额：%s", formatPrice(*signal.AccountBalance)))
+			lines = append(lines, fmt.Sprintf("账户余额：%s", display.FormatPrice(*signal.AccountBalance)))
 		}
 	case "ADD":
-		lines = append(lines, fmt.Sprintf("加仓价格: %s", formatPrice(signal.Price)))
+		lines = append(lines, fmt.Sprintf("加仓价格: %s", display.FormatPrice(signal.Price)))
 		if line := sizeLine("ADD", signal.Quantity, signal.AmountMarginRatio); line != "" {
 			lines = append(lines, line)
 		}
@@ -65,19 +64,19 @@ func Format(signal *Signal, opts ...FormatOptions) string {
 			lines = append(lines, fmt.Sprintf("杠杆: %dx", signal.Leverage))
 		}
 	case "REDUCE":
-		lines = append(lines, fmt.Sprintf("减仓价格: %s", formatPrice(signal.Price)))
+		lines = append(lines, fmt.Sprintf("减仓价格: %s", display.FormatPrice(signal.Price)))
 		if line := sizeLine("REDUCE", signal.Quantity, signal.PosMarginRatio); line != "" {
 			lines = append(lines, line)
 		}
 		lines = appendAvgPrice(lines, opt.AvgPrice)
 		if signal.PnL != nil {
-			lines = append(lines, fmt.Sprintf("减仓盈亏: %s", formatPrice(*signal.PnL)))
+			lines = append(lines, fmt.Sprintf("减仓盈亏: %s", display.FormatPrice(*signal.PnL)))
 		}
 		if signal.AccountBalance != nil {
-			lines = append(lines, fmt.Sprintf("账户余额：%s", formatPrice(*signal.AccountBalance)))
+			lines = append(lines, fmt.Sprintf("账户余额：%s", display.FormatPrice(*signal.AccountBalance)))
 		}
 	default:
-		lines = append(lines, fmt.Sprintf("价格: %s", formatPrice(signal.Price)))
+		lines = append(lines, fmt.Sprintf("价格: %s", display.FormatPrice(signal.Price)))
 		if line := sizeLine("", signal.Quantity, signal.AmountMarginRatio); line != "" {
 			lines = append(lines, line)
 		}
@@ -129,7 +128,7 @@ func appendAvgPrice(lines []string, avgPrice *float64) []string {
 	if avgPrice == nil || *avgPrice <= 0 {
 		return lines
 	}
-	return append(lines, fmt.Sprintf("平均单价: %s", formatPrice(*avgPrice)))
+	return append(lines, fmt.Sprintf("平均单价: %s", display.FormatPrice(*avgPrice)))
 }
 
 func closeSizeLine(quantity, posMarginRatio *float64) string {
@@ -190,19 +189,6 @@ func formatPercent(ratio float64) string {
 	return fmt.Sprintf("%.2f%%", ratio*100)
 }
 
-// formatPrice renders a price for display. Values >= 1 keep two decimals for
-// readability; smaller values use the shortest exact representation so tiny
-// prices like 0.00000059 are not collapsed to 0.00.
-func formatPrice(v float64) string {
-	if v == 0 {
-		return "0.00"
-	}
-	if math.Abs(v) >= 1 {
-		return strconv.FormatFloat(v, 'f', 2, 64)
-	}
-	return strconv.FormatFloat(v, 'f', -1, 64)
-}
-
 func trimQuote(symbol string) string {
 	symbol = strings.ToUpper(symbol)
 	for _, suffix := range []string{"USDT", "USDC", "BUSD", "USD"} {