fix(定时轮): 初始化失败返回错误并补充单测

- NewTimingWheelService 改为返回 error，避免 panic

- ProvideTimingWheelService 透传 error 并更新 wire 生成代码

- 补充定时任务调度/取消/周期任务相关单元测试

backend/internal/service/wire.go

@@ -65,10 +65,13 @@ func ProvideAccountExpiryService(accountRepo AccountRepository) *AccountExpirySe
 }
 
 // ProvideTimingWheelService creates and starts TimingWheelService
-func ProvideTimingWheelService() *TimingWheelService {
-	svc := NewTimingWheelService()
+func ProvideTimingWheelService() (*TimingWheelService, error) {
+	svc, err := NewTimingWheelService()
+	if err != nil {
+		return nil, err
+	}
 	svc.Start()
-	return svc
+	return svc, nil
 }
 
 // ProvideDeferredService creates and starts DeferredService