gh-36426: cleanup of gap3 interface file
This refreshes the modified file, mostly for pep8 compliance
also gathering doctests annotations
also changes two calls to `super`
### :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/36426
Reported by: Frédéric Chapoton
Reviewer(s): Kwankyu Lee
