refactor(accrual): 提取BuildLegRate/BuildEodPolicy消除EOD wrapper构造重复

EOD CompoundEod + SimpleEod 各有一份相同的FundingLegRate构造(3行)
和AccrualPolicy构造(5行), 共16行重复。

提取为:
- BuildLegRate(position, spread, effectiveFloat): 固定腿→Fixed, 浮动腿→Floating
- BuildEodPolicy(position, annualDays, isCompound): 算头算尾+重置周期

每个EOD wrapper从10行构造代码→2行调用, 净减12行
SwapModule零回归(7基线/510通过)

YLErpDAL/Modules/SwapModule/SwapDealService.cs

@@ -1339,6 +1339,16 @@ namespace YLErp.Modules.SwapModule
             throw new Exception($"获取不到{position.FloatRateUnderlyingCode}在{fixingDate:yyyy年MM月dd日}的价格");
         }
 
+        /// <summary>构造利率值对象：固定腿→Fixed(spread)，浮动腿→Floating(spread+fixing)。</summary>
+        private static FundingLegRate BuildLegRate(swap_position position, decimal spread, decimal effectiveFloat)
+            => string.IsNullOrEmpty(position.FloatRateUnderlyingCode)
+                ? FundingLegRate.Fixed(spread)
+                : FundingLegRate.Floating(spread, effectiveFloat);
+
+        /// <summary>构造 EOD 计息政策（算头算尾，重置周期取 position.interest_rest_days）。</summary>
+        private static AccrualPolicy BuildEodPolicy(swap_position position, int annualDays, bool isCompound)
+            => new AccrualPolicy(AccrualBoundary.Both, isCompound, position.interest_rest_days ?? 1, annualDays, position.IsAnnualized);
+
         /// <summary>
         /// 按重置周期切分利率段，每段记录 all-in 利率(spread+fixing)。返回 (分段列表, 末段浮动利率)。
         /// fetchAfterDate: 仅该日期之后的重置日才取 FR007（单利传 ValueDate，复利传 null 全程取）。
@@ -1478,16 +1488,8 @@ namespace YLErp.Modules.SwapModule
                 : 1m;
 
             // 纯数学下沉至 CompoundInterestAccrual.AccrueEod（DDD 命名 + 末位生产精度 12 舍入）。
-            var isFixedLeg = string.IsNullOrEmpty(position.FloatRateUnderlyingCode);
-            var legRate = isFixedLeg
-                ? FundingLegRate.Fixed(flowEvent.InterestRate)
-                : FundingLegRate.Floating(flowEvent.InterestRate, effectiveFloat);
-            var accrualPolicy = new AccrualPolicy(
-                convention: AccrualBoundary.Both,
-                isCompound: true,
-                resetPeriodDays: interestPeriod,
-                annualDays: annualDays,
-                isAnnualized: position.IsAnnualized);
+            var legRate = BuildLegRate(position, flowEvent.InterestRate, effectiveFloat);
+            var accrualPolicy = BuildEodPolicy(position, annualDays, isCompound: true);
 
             // 完整计息 trace：前后日期/基数/利率/重置标志全过程，经 SwapCalcTrace 常驻落盘（关键路径日志）。
             var interestTrace = new AccrualTrace();
@@ -1533,18 +1535,9 @@ namespace YLErp.Modules.SwapModule
 
             flowEvent.FloatRate = effectiveFloat;
 
-            // 纯数学下沉至 SimpleInterestAccrual（DDD 命名 + 末位生产精度 12 舍入），行为与上版逐字对齐。
-            // 利率构成按腿型封装：固定腿 → FixedRate；浮动腿 → Spread + IndexFixing（沿用旧实现 InterestRate+浮动利率 的口径）。
-            var isFixedLeg = string.IsNullOrEmpty(position.FloatRateUnderlyingCode);
-            var legRate = isFixedLeg
-                ? FundingLegRate.Fixed(flowEvent.InterestRate)
-                : FundingLegRate.Floating(flowEvent.InterestRate, effectiveFloat);
-            var accrualPolicy = new AccrualPolicy(
-                convention: AccrualBoundary.Both,
-                isCompound: false,
-                resetPeriodDays: position.interest_rest_days ?? 1,
-                annualDays: annualDays,
-                isAnnualized: position.IsAnnualized);
+            // 纯数学下沉至 SimpleInterestAccrual（末位生产精度 12 舍入）。
+            var legRate = BuildLegRate(position, flowEvent.InterestRate, effectiveFloat);
+            var accrualPolicy = BuildEodPolicy(position, annualDays, isCompound: false);
             // 完整计息 trace：收集器由适配器创建，随后经 SwapCalcTrace 常驻落盘（关键路径日志，无条件）。
             var interestTrace = new AccrualTrace();
             var result = SimpleInterestAccrual.AccrueEod(