gh-38257: some pep8 cleanup in four crystal files
a somewhat large scale pep8 cleanup in the 4 modified files in the
crystals folder
also a few minor code enhancements
### :memo: Checklist
- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
URL: https://github.com/sagemath/sage/pull/38257
Reported by: Frédéric Chapoton
Reviewer(s): David Coudert, Frédéric Chapoton
