Add unit tests for ExceptionEvaluator, ExceptionEvent, ExceptionHistory, and ExceptionObject models

- Implemented comprehensive unit tests for the ExceptionEvaluator service, covering various scenarios including matching exceptions, environment checks, and evidence references.
- Created tests for the ExceptionEvent model to validate event creation methods and ensure correct event properties.
- Developed tests for the ExceptionHistory model to verify event count, order, and timestamps.
- Added tests for the ExceptionObject domain model to ensure validity checks and property preservation for various fields.

src/Policy/__Tests/StellaOps.Policy.Gateway.Tests/StellaOps.Policy.Gateway.Tests.csproj

@@ -4,9 +4,26 @@
     <TargetFramework>net10.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+    <IsTestProject>true</IsTestProject>
   </PropertyGroup>
 
   <ItemGroup>
     <ProjectReference Include="../../StellaOps.Policy.Gateway/StellaOps.Policy.Gateway.csproj" />
   </ItemGroup>
-</Project>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
+    <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="3.0.2">
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+      <PrivateAssets>all</PrivateAssets>
+    </PackageReference>
+    <PackageReference Include="Moq" Version="4.20.72" />
+    <PackageReference Include="FluentAssertions" Version="8.0.1" />
+    <PackageReference Include="coverlet.collector" Version="6.0.4">
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+      <PrivateAssets>all</PrivateAssets>
+    </PackageReference>
+  </ItemGroup>
+</Project>