refactor(margin): 保证金去除'计息基数'错误概念, 改用余额建模

保证金就是保证金——有余额、有利率、有利息, 不存在'计息基数/Notional'概念。
现有代码把保证金塞进 InterestPrincipalFix 当计息腿处理是错误建模。

修正:
- 删除 MarginLeg.cs(CalcBalance/accrualFactor 是融资腿的概念, 不该用在保证金)
- 新增 MarginAccount.cs: 管理余额变动(Deposit追加/Withdraw释放), 不含计息
- MarginBalance: 注释去掉'计息基数', 改为'保证金余额'
- IMarginResolver.Resolve: 去掉 accrualFactor 参数(融资腿比例, 非保证金概念)
- CashMargin/CreditMargin/GuaranteeMargin: 同步去掉 accrualFactor
- 枚举注释: '计息余额' → '余额'

保证金利息由 SwapInterest 纯函数按 余额×利率×天数/年化 计算,
MarginAccount 只提供余额, 不掺计息逻辑。

验证: sln编译0错误, 全量486测试7失败(基线一致,零回归)。

UnitTestProject/Modules/SwapModule/Margin/MarginLegTest.cs

@@ -4,40 +4,53 @@ using YLErp.Modules.SwapModule.Margin;
 namespace UnitTestProject.Modules.SwapModule.Margin
 {
     /// <summary>
-    /// 保证金利息计提（MarginLeg）单测。验证计息余额计算，以及三种形态解析器可互换产余额。
-    /// 替换原 InterestLegStrategyTest 里的预付金（PrepayLeg）用例——预付金已迁出利息腿限界上下文。
+    /// 保证金账户(MarginAccount)单测。验证余额变动（追加/释放/返还）。
+    /// 保证金就是保证金——有余额、有利率、有利息，不存在"计息基数/Notional"概念。
     /// </summary>
     [TestClass]
     public class MarginLegTest
     {
-        private const decimal Balance = 2_000_000m;
+        private const decimal Opening = 2_000_000m;
+
+        #region MarginAccount 余额变动
 
         [TestMethod]
-        public void 计息余额_默认不缩放_等于保证金全额()
+        public void 账户_初始余额等于期初保证金()
         {
-            var leg = new MarginLeg();
-            var r = leg.CalcBalance(Balance);
-            Assert.AreEqual(Balance, r.Balance, "默认不缩放，余额=保证金全额");
+            var account = new MarginAccount(new MarginBalance(Opening));
+            Assert.AreEqual(Opening, account.Balance.Balance);
         }
 
         [TestMethod]
-        public void 计息余额_部分释放_按适用比例缩放()
+        public void 账户_追加保证金_余额增加()
         {
-            var leg = new MarginLeg();
-            var r = leg.CalcBalance(Balance, 0.5m);
-            Assert.AreEqual(1_000_000m, r.Balance, "部分释放：余额×适用比例");
+            var account = new MarginAccount(new MarginBalance(Opening));
+            account.Deposit(500_000m);
+            Assert.AreEqual(2_500_000m, account.Balance.Balance);
         }
 
         [TestMethod]
-        public void 计息余额_零适用比例_为零()
+        public void 账户_释放保证金_余额减少()
         {
-            var leg = new MarginLeg();
-            var r = leg.CalcBalance(Balance, 0m);
-            Assert.AreEqual(0m, r.Balance);
+            var account = new MarginAccount(new MarginBalance(Opening));
+            account.Withdraw(800_000m);
+            Assert.AreEqual(1_200_000m, account.Balance.Balance);
         }
 
         [TestMethod]
-        public void 三种形态解析器_均可互换产出余额()
+        public void 账户_释放超过余额_不低于零()
+        {
+            var account = new MarginAccount(new MarginBalance(Opening));
+            account.Withdraw(3_000_000m);
+            Assert.AreEqual(0m, account.Balance.Balance, "保证金余额不低于零");
+        }
+
+        #endregion
+
+        #region 三种保证金形态解析器
+
+        [TestMethod]
+        public void 三种形态解析器_各自返回正确Form和余额()
         {
             IMarginResolver cash = new CashMargin();
             IMarginResolver credit = new CreditMargin();
@@ -47,9 +60,11 @@ namespace UnitTestProject.Modules.SwapModule.Margin
             Assert.AreEqual(MarginForm.Credit, credit.Form);
             Assert.AreEqual(MarginForm.Guarantee, guarantee.Form);
 
-            Assert.AreEqual(1_000_000m, cash.Resolve(Balance, 0.5m).Balance);
-            Assert.AreEqual(1_000_000m, credit.Resolve(Balance, 0.5m).Balance);
-            Assert.AreEqual(1_000_000m, guarantee.Resolve(Balance, 0.5m).Balance);
+            Assert.AreEqual(Opening, cash.Resolve(Opening).Balance);
+            Assert.AreEqual(Opening, credit.Resolve(Opening).Balance);
+            Assert.AreEqual(Opening, guarantee.Resolve(Opening).Balance);
         }
+
+        #endregion
     }
 }