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Inverted ragged list
Given a ragged list of positive integers, where the maximum depth is \$d_\text{max}\$, return the same list, except for every element \$e\$, its depth is \$d_\text{max}+1-d_e\$ (where \$d_e\$ is the depth of that element).
Test cases
[] -> []
[[1,2],3,4] -> [1,2,[3,4]]
[3,[2,...