Update Zip to 2.1.1 and Nodal to 0.4.0

Use consistent String types for element/container names to match
Nodal's new explicit overloads.

Update README to include Production specification support

Squashed commit of the following:

commit 0b7a941
Author: Tomas Franzén <[email protected]>
Date:   Sat Oct 18 14:18:15 2025 +0200

    Add docs for PackageReader and PackageWriter

commit a1659d8
Author: Tomas Franzén <[email protected]>
Date:   Sat Oct 18 14:03:23 2025 +0200

    Add docs for ModelLoader

commit 22edd3a
Author: Tomas Franzén <[email protected]>
Date:   Thu Sep 11 18:31:09 2025 +0200

    Add support for the 3MF Production extension

    Also add ModelLoader.

Add support for custom attributes for item and remove built-in suppor…

…t for Prusa's printable attribute