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.

quantower/Quantower.Tests.csproj

@@ -8,6 +8,10 @@
     <IsPackable>false</IsPackable>
     <IsTestProject>true</IsTestProject>
     <EnableDefaultCompileItems>false</EnableDefaultCompileItems>
+    <!-- Coverage configuration for coverlet.msbuild -->
+    <CollectCoverage>true</CollectCoverage>
+    <CoverletOutputFormat>opencover</CoverletOutputFormat>
+    <CoverletOutput>TestResults/coverage.opencover.xml</CoverletOutput>
   </PropertyGroup>
 
   <ItemGroup>
@@ -17,6 +21,10 @@
 
   <ItemGroup>
     <PackageReference Include="coverlet.collector" Version="6.0.4" />
+    <PackageReference Include="coverlet.msbuild" Version="6.0.2">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>
+    </PackageReference>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
     <PackageReference Include="xunit" Version="2.9.3" />
     <PackageReference Include="xunit.runner.visualstudio" Version="3.0.0">
@@ -48,4 +56,4 @@
     <Compile Include="IndicatorExtensions.cs" />
   </ItemGroup>
 
-</Project>
+</Project>