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

### 📝 Checklist

- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
    
URL: #38257
Reported by: Frédéric Chapoton
Reviewer(s): David Coudert, Frédéric Chapoton