refactor: 共享请求管道、按需懒加载、流式内存护栏与连接池治理

- 抽取 ApiRequestPipeline 单例，44 个路由文件共享同一实例
- Handler/Adapter 模块级 __getattr__ 延迟导入，减少启动时间
- 新增 ensure_stream_buffer_limit() 流式内存护栏（16MB 单行 / 32MB 总量）
- HTTP 空闲连接清理与 curl_cffi LRU 会话池
- ensure_providers_bootstrapped 按需引导指定 provider_types
- Usage 事件序列化迁移至 msgpack，Redis codec 隔离
- 启动预热任务（/readyz 就绪门控）与优雅关闭
- 通知邮件模块独立开关与 SMTP 配置校验
- CryptoService DCL 线程安全修复
- 通知模块开关 DB 查询 30s 内存缓存
- /readyz 对 unknown 状态返回 503
- 预热关闭 5s 超时保护
- 预热适配器逐个 try-except 容错
- FormatConversionRegistry 哨兵模式防并发重复物化
- 流式缓冲检查无条件执行

Closes #230

Co-authored-by: AAEE86 <[email protected]>

tests/services/test_format_conversion_health_buckets.py

@@ -57,11 +57,12 @@ async def test_executor_records_health_by_provider_format() -> None:
         patch("src.services.request.executor.RequestCandidateService.mark_candidate_started"),
         patch("src.services.request.executor.RequestCandidateService.mark_candidate_success"),
         patch("src.services.request.executor.get_adaptive_reservation_manager") as mock_res_mgr,
-        patch("src.services.request.executor.health_monitor.record_success") as record_success,
+        patch("src.services.request.executor.get_health_monitor") as mock_get_health_monitor,
     ):
         mock_res_mgr.return_value.calculate_reservation.return_value = MagicMock(
             ratio=0.0, phase="stable", confidence=1.0
         )
+        record_success = mock_get_health_monitor.return_value.record_success
 
         executor = RequestExecutor(
             db=db, concurrency_manager=concurrency_manager, adaptive_manager=adaptive_manager
@@ -100,8 +101,9 @@ async def test_error_classifier_records_failure_by_provider_format() -> None:
     key.id = "k1"
 
     with patch(
-        "src.services.orchestration.error_handler.health_monitor.record_failure"
-    ) as record_failure:
+        "src.services.orchestration.error_handler.get_health_monitor"
+    ) as mock_get_health_monitor:
+        record_failure = mock_get_health_monitor.return_value.record_failure
         await classifier.handle_retriable_error(
             error=RuntimeError("boom"),
             provider=provider,