gh-36880: various details fixed in coding (ruff, pep8, links in the doc)
this is fixing various details in the coding folder
- ruff suggestions
- doc indentation
- links to errors in the doc
### :memo: Checklist
- [x] The title is concise, informative, and self-explanatory.
- [x] The description explains in detail what this PR is about.
URL: https://github.com/sagemath/sage/pull/36880
Reported by: Frédéric Chapoton
Reviewer(s): David Coudert
