fix nullability of AssemblyEnumerator.GetTypes

[SimonCropp]

• ReflectionTypeLoadException.Types returns Type?[] https://learn.microsoft.com/en-us/dotnet/api/System.Reflection.ReflectionTypeLoadException.Types?view=net-9.0 to return type of AssemblyEnumerator.GetTypes is incorrect
• ReflectionTypeLoadException.LoaderExceptions returns a Exception?[] https://learn.microsoft.com/en-us/dotnet/api/system.reflection.reflectiontypeloadexception.loaderexceptions?view=net-9.0 so the null check is a no-op. i assume the intent is to "log a warning and continue with loaded types if there are LoaderExceptions"
• fixed a bug where GetAssemblyInfo would redundantly attempt to IsDerivedAttributeDefined for a null value, and then catch the result null ref excpetion