Add parameterized cube module

[crow]

This PR adds a new parameterized cube module that can be used as a building block for other designs. The module includes the following features:

• Customizable dimensions (x, y, z)
• Optional centering
• Configurable wall thickness for hollow cubes
• Optional rounded corners with adjustable radius
• Input validation
• Commented example usage

This can be useful for:

1. Creating basic building blocks for more complex designs
2. Rapid prototyping of cube-based structures
3. Creating enclosures with configurable wall thickness
4. Making rounded-corner variants of existing cube designs

The module is well-documented and includes example usage patterns in comments.