feat: Make the stub partial

Author: linkdotnet

src/bunit.generators/Web.Stubs/StubGenerator.cs

@@ -103,7 +103,7 @@ private static bool GenerateStubComponent(StubClassInfo classInfo, SourceProduct
 		var sourceBuilder = new StringBuilder();
 
 		sourceBuilder.AppendLine($"namespace {classInfo.TargetTypeNamespace};");
-		sourceBuilder.AppendLine($"public class {classInfo.StubClassName} : Microsoft.AspNetCore.Components.ComponentBase");
+		sourceBuilder.AppendLine($"public partial class {classInfo.StubClassName} : Microsoft.AspNetCore.Components.ComponentBase");
 		sourceBuilder.Append("{");
 
 		foreach (var member in targetTypeSymbol