Clean up voxel shape transforms

[jjhembd]

Description

This PR cleans up some internal transforms for voxel shape bounds.

The VoxelShape classes had separate vec2 uniforms for the bounds along each dimension, each uniform containing a scale and a translation. However, since #12933, the translation was not used in the shader. This PR combines the 3 scalars into a single vec3 uniform.

A few inline comments were added to clarify some of the bounds transform calculations.

Issue number and link

Resolves #12782.

Testing plan

Author checklist

• I have submitted a Contributor License Agreement
• I have added my name to CONTRIBUTORS.md
• I have updated CHANGES.md with a short summary of my change
• I have added or updated unit tests to ensure consistent code coverage
• I have updated the inline documentation, and included code examples where relevant
• I have performed a self-review of my code

AI acknowledgment

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If yes, I used the following Model(s):

Claude Sonnet 4

[github-actions]

Thank you for the pull request, @jjhembd!

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