Add R² and SMAPE error metrics with comprehensive tests and documentation

- Introduced R² (Coefficient of Determination) metric with detailed mathematical foundation, performance profile, and usage examples.
- Implemented SMAPE (Symmetric Mean Absolute Percentage Error) metric, addressing asymmetry in MAPE with symmetric error calculations.
- Added unit tests for SMAPE covering various scenarios including edge cases and input validation.
- Enhanced Dema class to correctly handle event publishing with isNew parameter.
- Updated Quantower test project to include coverage configuration for better test reporting.

lib/trends/dema/Dema.cs

@@ -97,7 +97,7 @@ public sealed class Dema : AbstractBase, IDisposable
         if (double.IsNaN(val))
         {
             Last = new TValue(input.Time, double.NaN);
-            PubEvent(Last);
+            PubEvent(Last, isNew);
             return Last;
         }
 
@@ -108,7 +108,7 @@ public sealed class Dema : AbstractBase, IDisposable
 
         double result = 2 * e1 - e2;
         Last = new TValue(input.Time, result);
-        PubEvent(Last);
+        PubEvent(Last, isNew);
         return Last;
     }
 
@@ -337,4 +337,4 @@ public sealed class Dema : AbstractBase, IDisposable
     }
 
     private void Handle(object? sender, in TValueEventArgs e) => Update(e.Value, e.IsNew);
-}
+}