some cython-linting in modular/ folder

[fchapoton]

📚 Description

This fixes some of the issues found by cython-lint in the modular folder. The command used was

cython-lint --ignore=E501,E265,E231,E127,E266,E741 src/sage/modular/

📝 Checklist

• The title is concise, informative, and self-explanatory.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation accordingly.

⌛ Dependencies

[github-actions]

Documentation preview for this PR is ready! 🎉
Built with commit: ea35699

[dcoudert]

You have not considered the comments I made, but it can be done in a future ticket.

[fchapoton]

You have not considered the comments I made, but it can be done in a future ticket.

heu, pardon, mais quels commentaires ?

[dcoudert]

J'avais fait des propositions de modifications du code du type (-cc,dd,&bb,&aa)) -> (-cc, dd, &bb, &aa), un for i from 0 <= i < k: qui reste, etc. Si tu ne vois pas ça sur la page de la pull request, forcément tu ne peux pas en tenir compte.