refactor(swap-test): 抽取 TestableSwapEodPositionService 公共基类收敛重复 Stub

- 新建 TestableSwapEodPositionService 收敛 8/8 Stub 重复的高频 override
  (PersistEodSwapPosition/SaveAllChanges/GetCurrencyRate/AddClientCash)
  + 统一 OptUserInfo 构造 + PersistedPositions/SaveChangesCount 输出捕获
- SwapEodPositionService.DealInterests 改 protected virtual（行为零变化）
- 8 个 ScenarioTest 改为继承基类，删除重复 override
- 消灭 DealInterestsScenarioTest/DealInterestsGoldenReplayTest 的反射调用
  (typeof().GetMethod().Invoke → 直接调用 DealInterests)

验证：dotnet build 0 错误；dotnet test SwapModule 284通过/6跳过/0失败

UnitTestProject/Modules/SwapModule/MultiUnwindDividendConservationTest.cs

@@ -40,11 +40,11 @@ namespace YLErp.Modules.SwapModule
         /// CalcBondPayment 改为按天数 × 持仓线性函数，使 TdPosiDividend 真实随
         /// "天数 × 剩余持仓"变化——这是验证多日递推守恒的前提。
         /// </summary>
-        private sealed class StubEodService : SwapEodPositionService
+        private sealed class StubEodService : TestableSwapEodPositionService
         {
             private readonly decimal _dailyRatePerUnit;
 
-            public StubEodService(decimal dailyRatePerUnit) : base(new OptUserInfo(0, nameof(MultiUnwindDividendConservationTest), OptUserFrom.UnitTest))
+            public StubEodService(decimal dailyRatePerUnit) : base(nameof(MultiUnwindDividendConservationTest))
             {
                 _dailyRatePerUnit = dailyRatePerUnit;
             }
@@ -66,14 +66,6 @@ namespace YLErp.Modules.SwapModule
                 return 1.00m;
             }
 
-            protected override void SaveAllChanges() { }
-
-            // 注意：UpdateEodPosition.cs:1645 直接 new EodCurrencyRateService，不走此 seam；
-            // 但 trade.QuoteCurrency == trade.SettlementCurrency == "CNY" 时，
-            // EodCurrencyRateService.GetEodCurrencyRate 会在查库前短路返回 Rate=1（cs:268-281）
-            protected override double GetCurrencyRate(string quoteCurrency, string settlementCurrency, DateTime valueDate, bool seekPreday, CurrencyRateType currencyRateType)
-                => 1.0;
-
             // 暴露 protected UpdateEodPosition（参考 GLMS20260105GoldenTest.ReplayStubService:244）
             public eod_swap_position ExecuteUpdateEodPosition(
                 swap_position swapPosition, eod_swap_position eod, trade td,