Document and refactor dodeca.rs

[patowen]

Fixes #381

This PR makes the following changes to the dodeca module:

• LazyLock is used instead of OnceLock (This change is also made in cursor.rs)
• Side and Vertex have a VALUES array allowing for easier conversion between integers and enum values
• VERTEX_COUNT and SIDE_COUNT have been replaced with Vertex::COUNT and Side::COUNT
• Vertex::from_sides now takes in an array instead of 3 separate parameters for consistency with Vertex::canonical_sides
• Arrays are now initialized to their final values when it makes sense to do so (instead of being initialized to a dummy value and then filled in). This utilizes array::from_fn and array::map in various places.
• Complicated math is better explained in code comments
• Some implementations are replaced with simpler implementations, such as is_facing, ADJACENT, and SIDES_TO_VERTEX

Changes in other modules are for compatibility with the changes to dodeca.