feat(data/list/forall2): add `list.forall₂_iff_nth_le` (#16073)
Characterization of `list.forall₂` with respect to `list.nth_le` on all positions.
Co-authored-by: madvorak <dvorakmartinbridge@seznam.cz>
Co-authored-by: Martin Dvořák <dvorakmartinbridge@seznam.cz>
Co-authored-by: Eric Wieser <wieser.eric@gmail.com>
