fix: mark function pointer types as stubs

Function pointer types are synthetic types created during dependency
resolution, not types directly loaded from assemblies. Setting
isStub=true ensures they are correctly classified as referenced
types rather than primary architecture types.

Signed-off-by: Alexander Linne <alexander.linne@tngtech.com>

Author: alexanderlinne

ArchUnitNET/Loader/TypeFactory.cs

@@ -432,7 +432,7 @@ FunctionPointerType functionPointerType
                 Public,
                 false,
                 false,
-                false,
+                true,
                 false
             );
             var returnTypeInstance = GetOrCreateStubTypeInstanceFromTypeReference(