I *strongly* believe the answer is not reasonable using phoboes
tools; but Im going to leave it as an open question before I get
started on something from scratch.
Given well compliant phoboes-style ranges and a `ref string or
retro!string` that starts with '(',')','[',']','{','}', modify
that string so that you a) find the matching pair, b) return a
list of indexs for where the top level commas are
"(foo([1,2]),bar!"\","(((())))foobar" =>
"(foo([1,2]),bar!"\","(((())))",[12]
retro("abc[1,2,3,4,"❤️❤️❤️❤️","\","]") => "[1,2,3,4,"❤️❤️❤️❤️","\","]",
[2,4,6,8,35]
