Fix CI build failures by disabling parallel builds for Core project to avoid analyzer locking issues

Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

Author: Copilot

src/ModelContextProtocol.Core/ModelContextProtocol.Core.csproj

@@ -8,6 +8,8 @@
     <Description>Core .NET SDK for the Model Context Protocol (MCP)</Description>
     <PackageReadmeFile>README.md</PackageReadmeFile>
     <AllowUnsafeBlocks>True</AllowUnsafeBlocks>
+    <!-- Disable parallel builds to avoid analyzer locking issues during multi-targeted builds -->
+    <BuildInParallel>false</BuildInParallel>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(TargetFramework)' != 'netstandard2.0'">
@@ -51,13 +53,12 @@
   <ItemGroup>
     <ProjectReference Include="..\ModelContextProtocol.SourceGenerators\ModelContextProtocol.SourceGenerators.csproj"
                       OutputItemType="Analyzer"
-                      ReferenceOutputAssembly="false"
-                      SetTargetFramework="TargetFramework=netstandard2.0" />
+                      ReferenceOutputAssembly="false" />
   </ItemGroup>
 
   <!-- Package the analyzer DLL into the NuGet package -->
   <ItemGroup>
-    <None Include="$(ArtifactsDir)bin\ModelContextProtocol.SourceGenerators\netstandard2.0\ModelContextProtocol.SourceGenerators.dll" 
+    <None Include="$(ArtifactsDir)bin\ModelContextProtocol.SourceGenerators\$(Configuration)\netstandard2.0\ModelContextProtocol.SourceGenerators.dll" 
           Pack="true" 
           PackagePath="analyzers/dotnet/cs" 
           Visible="false" />