test: add comprehensive coverage and fix EnumeratorIList bug (#100)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: glennawatson <5834289+glennawatson@users.noreply.github.com>

Author: Copilot

src/Directory.Build.props

@@ -21,6 +21,7 @@
     <IsTestProject>$(MSBuildProjectName.Contains('Tests'))</IsTestProject>
     <DebugType>embedded</DebugType>
     <NoWarn>$(NoWarn);SA1010</NoWarn>
+    <WarningsAsErrors>Nullable</WarningsAsErrors>
 
     <!-- Publish the repository URL in the built .nupkg (in the NuSpec <Repository> element) -->
     <PublishRepositoryUrl>true</PublishRepositoryUrl>

src/Directory.Packages.props

@@ -26,6 +26,7 @@
     <PackageVersion Include="NUnit" Version="4.4.0" />
     <PackageVersion Include="NUnit3TestAdapter" Version="5.2.0" />
     <PackageVersion Include="NUnit.Analyzers" Version="4.11.2" />
+    <PackageVersion Include="DynamicData" Version="9.4.1" />
   </ItemGroup>
 
   <Import