Add shapemoves subpackage based on conway

[janbridley]

Description

After some review, I've decided it makes more sense to include my shape move operators in coxeter rather than as a separate conway package. I get a fair few requests for the ability to modify geometries, and would like to bundle these features into this package.

Current Plan

I'm starting with a few example methods (vertex truncation and pyramid augmentation) to get a sense for the appropriate layout, which I will expand into the rest of the operators I have implemented in time. Many of the families in conway.seeds can be ported to coxeter.families, which minor changes to the documentation.

Longer term, coxeter's families provide a nice manner by which I can define composable high-dimensional families, the continuous extension of the original "string sequence" operations (see example). This was the ultimate goal of conway, but consolidating the code in coxeter minimizes code duplication while maximizing visibility.

For this PR:

• Port truncate/kis
• Port tests for truncate/kis
• Update docs for truncate/kis - show examples and explain uniformity with truncated dipyramid
• Port (Base)|(Tip)TruncatedDipyramid family (based on Sangmin clathrate paper)
• Port CanonicalTrapezohedron family and tests

Motivation and Context

While the generality of code in conway isn't a 1 to 1 match with coxeter, there are portions of it that I'd like to have generally available. I hope this refactor will reduce confusion for users hoping to modify geometries, and it will certainly reduce the total administration required for releases and CI updates. More generally though, Conway already relies on coxeter for computing intermediate properties of multiple shape moves. Tying conway more tightly into coxeter will allow for better performance for sequences of moves, and will give me a chance to finally enable incremental vertex addition as an option for Convex Polyhedra

Types of Changes

• Documentation update
• Bug fix
• New feature
• Breaking change¹

¹The change breaks (or has the potential to break) existing functionality.

Checklist:

• I am familiar with the Contributing Guidelines.
• I agree with the terms of the Contributor Agreement.
• The changes introduced by this pull request are covered by existing or newly introduced tests.
• I have updated the changelog and the credits.