Managed struct types fix

✅ Fixed serialization of managed struct types
✅ Minor performance improvements

Initial release

✅ Primitive types (except object): string, bool, int, uint, float, double, etc.
✅ Nullable value types: Nullable<T> or T? for short, where T : struct
✅ Unmanaged types: eg. System.Numerics.Vector2, and all unmanaged value types
✅ .NET arrays: T[], T[,], T[,,], etc.
✅ .NET collections: List<T>, IList<T>, ICollection<T>, IEnumerable<T>, etc.
✅ .NET dictionaries: Dictionary<TKey, TValue>, IDictionary<TKey, TValue>, etc.
✅ Other .NET types: BitArray
✅ Attributes to specify how to serialize objects and what members to include