perf(http): 修复响应日期格式化每次重建 ICU formatter 导致的 CPU 热点

formatResponseDateTime 在函数内部 `new Intl.DateTimeFormat(...)`，而
buildSuccessPayload 会对每个成功响应的每个日期字段调用它。ICU formatter
单次构造约 0.5~0.8ms，V8 CPU 采样显示该函数占后端主线程约 30% CPU（约 0.33 核）。

改动：
- formatter 提到模块级只构造一次；formatToParts 直取字段，去掉
  Object.fromEntries + filter + map 的三次分配
- isIsoDateTimeString 增加 O(1) 位置预判，避免对每个字段值跑正则
- normalizeResponseDateTime 用显式循环替代 entries/fromEntries 双重分配
- 同类问题一并修复：open-91 formatOpen91ExpireTime、redeem formatGrantTime

输出逐字节一致：新增等价性测试，以修复前实现为参考覆盖跨时区/毫秒/
闰日/跨年/非法日期语料。同形态响应（200 行 × 6 日期字段）实测
35.2ms → 2.6ms（13.6x）。

apps/backend/src/services/open-91/response.ts

@@ -3,6 +3,21 @@ import { OPEN_91_DEFAULT_FAIL_CODE, OPEN_91_SUCCESS_MESSAGE } from './config.js'
 import { isOpen91FailedTaskStatus } from '../../domain/task-status.js'
 import { normalizeOpen91String } from './payload.js'
 
+/**
+ * 模块级只构造一次：`new Intl.DateTimeFormat()` 每次都会重新装载 ICU locale 数据，
+ * 单次约 0.5ms。该格式化器按响应字段逐条调用，放在函数内会随响应行数线性放大。
+ */
+const OPEN_91_EXPIRE_FORMATTER = new Intl.DateTimeFormat('zh-CN', {
+  timeZone: 'Asia/Shanghai',
+  year: 'numeric',
+  month: '2-digit',
+  day: '2-digit',
+  hour: '2-digit',
+  minute: '2-digit',
+  second: '2-digit',
+  hourCycle: 'h23',
+})
+
 export function buildOpen91SuccessResponse(data: unknown, message = OPEN_91_SUCCESS_MESSAGE) {
   return {
     code: 200,
@@ -57,18 +72,12 @@ export function formatOpen91ExpireTime(value: unknown = '') {
     return normalized
   }
 
-  const parts = new Intl.DateTimeFormat('zh-CN', {
-    timeZone: 'Asia/Shanghai',
-    year: 'numeric',
-    month: '2-digit',
-    day: '2-digit',
-    hour: '2-digit',
-    minute: '2-digit',
-    second: '2-digit',
-    hourCycle: 'h23',
-  }).formatToParts(date)
+  const parts = OPEN_91_EXPIRE_FORMATTER.formatToParts(date)
 
-  const byType = Object.fromEntries(parts.map((part) => [part.type, part.value]))
+  const byType: Record<string, string> = {}
+  for (const part of parts) {
+    if (part.type !== 'literal') byType[part.type] = part.value
+  }
   return `${byType.year}-${byType.month}-${byType.day} ${byType.hour}:${byType.minute}:${byType.second}`
 }
 

apps/backend/src/services/redeem/certificate-service.ts

@@ -842,6 +842,20 @@ export async function findCertificateOrThrow(certNo: string): Promise<RedeemCert
   return row
 }
 
+/**
+ * 模块级只构造一次：`new Intl.DateTimeFormat()` 每次都会重新装载 ICU locale 数据，
+ * 单次约 0.5ms。凭证按条签发/查询时会逐条调用 formatGrantTime，放在函数内会线性放大。
+ */
+const GRANT_TIME_FORMATTER = new Intl.DateTimeFormat('zh-CN', {
+  timeZone: 'Asia/Shanghai',
+  year: 'numeric',
+  month: '2-digit',
+  day: '2-digit',
+  hour: '2-digit',
+  minute: '2-digit',
+  second: '2-digit',
+})
+
 /** 平台的 grant_time 形如 `YYYY-MM-DD HH:MM:SS`（北京时间）。 */
 export function formatGrantTime(iso: string): string {
   const date = new Date(iso)
@@ -849,18 +863,12 @@ export function formatGrantTime(iso: string): string {
     return ''
   }
 
-  const parts = new Intl.DateTimeFormat('zh-CN', {
-    timeZone: 'Asia/Shanghai',
-    year: 'numeric',
-    month: '2-digit',
-    day: '2-digit',
-    hour: '2-digit',
-    minute: '2-digit',
-    second: '2-digit',
-  }).formatToParts(date)
+  const parts = GRANT_TIME_FORMATTER.formatToParts(date)
 
-  const pick = (type: Intl.DateTimeFormatPartTypes) =>
-    parts.find((part) => part.type === type)?.value || ''
+  const byType: Record<string, string> = {}
+  for (const part of parts) {
+    if (part.type !== 'literal') byType[part.type] = part.value
+  }
 
-  return `${pick('year')}-${pick('month')}-${pick('day')} ${pick('hour')}:${pick('minute')}:${pick('second')}`
+  return `${byType.year}-${byType.month}-${byType.day} ${byType.hour}:${byType.minute}:${byType.second}`
 }