various list-comprehension in combinat (ruff PERF)

[fchapoton]

following some ruff --select=PERF src/sage/combinat suggestions

i.e. using more often list comprehension where possible

(also turned one method to an iterator)

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[github-actions]

Documentation preview for this PR (built with commit 32799a6; changes) is ready! 🎉

[mantepse]

see #35715 for the doctest error in rings, which is therefore unrelated.

[mantepse]

Thank you!