feat(data/list/basic): fold[rl] recursion principles (#7079)
feat(data/list/basic): fold[rl] recursion principles (#7079)





Co-authored-by: Yakov Pechersky <9925c0c20eafe10b1eaac37c5fe124dc0b28ca8c@users.noreply.github.com>

leanprover-community/mathlib,leanprover-community/mathlib