perf(engine): replace magic-string RequiredAttribute match with type check in ConstructorHelper

TUnit.Engine/Discovery/ConstructorHelper.cs

@@ -126,9 +126,29 @@ public static bool HasRequiredProperties([DynamicallyAccessedMembers(Dynamically
 
         // Also check individual properties for RequiredAttribute (older approach)
         var properties = type.GetProperties(BindingFlags.Public | BindingFlags.Instance);
-        return properties.Any(p => p.GetCustomAttributes().Any(a => a.GetType().Name == "RequiredAttribute"));
+        foreach (var property in properties)
+        {
+            if (HasRequiredAttribute(property))
+            {
+                return true;
+            }
+        }
+
+        return false;
     }
 
+    // System.ComponentModel.DataAnnotations.RequiredAttribute, resolved once. It lives in a separate
+    // assembly that isn't referenced on netstandard2.0, so we look it up by name instead of a compile-time
+    // type reference. Null when the type can't be loaded (e.g. the assembly isn't present).
+    private static readonly Type? RequiredAttributeType =
+        Type.GetType("System.ComponentModel.DataAnnotations.RequiredAttribute, System.ComponentModel.Annotations")
+        ?? Type.GetType("System.ComponentModel.DataAnnotations.RequiredAttribute, System.ComponentModel.DataAnnotations");
+
+    private static bool HasRequiredAttribute(PropertyInfo property) =>
+        // IsDefined checks metadata tokens only — no attribute instances are materialised.
+        // It matches subclasses of RequiredAttributeType, same as the previous IsInstanceOfType.
+        RequiredAttributeType is not null && property.IsDefined(RequiredAttributeType, inherit: true);
+
     /// <summary>
     /// Tries to initialize required properties on an instance
     /// </summary>
@@ -145,7 +165,7 @@ public static void InitializeRequiredProperties(
         {
             // In C# 11+, required properties are marked with RequiredMemberAttribute at the member level
             var isRequired = property.GetCustomAttribute<System.Runtime.CompilerServices.RequiredMemberAttribute>() != null ||
-                            property.GetCustomAttributes().Any(a => a.GetType().Name == "RequiredAttribute");
+                            HasRequiredAttribute(property);
 
             // Also check if property is marked with 'required' modifier by checking if it's init-only and the type has RequiredMemberAttribute
             if (!isRequired && property is { CanWrite: true, SetMethod.IsSpecialName: true } &&