gh-39053: small-scale refresh for the sandpile file
    
fix some pep8, ruff, mypy warnings

break some of the many long lines

minor changes in the code

### 📝 Checklist

- [ ] The title is concise and informative.
- [ ] The description explains in detail what this PR is about.
    
URL: #39053
Reported by: Frédéric Chapoton
Reviewer(s): David Coudert, Frédéric Chapoton

Author: Release Manager