• Added support for the 3MF production extension which, lets a 3MF package contain multiple model files. (See PackageReader.model(at:), PackageWriter.addAdditionalModel(_:named:)).
• Added ModelLoader, an easier way to load a model without worrying about 3MF details. It resolves components as well as cross‑model references and produces a flattened, render‑ready representation of meshes and build items.
• Item now supports reading and writing custom attributes.
• PackageReader now uses Zip's .readOnly mode.

Initial release