Row-pivoted Bareiss determinant soundness, exposed against Mathlib's determinant for downstream Mathlib-side callers.
The row-pivoted Bareiss determinant equals the executable Leibniz
determinant on integer square matrices. Proven Mathlib-side by composing
bareiss_eq_mathlib_det with det_eq, so it holds unconditionally (with no
side hypothesis) and is the preferred surface for downstream Mathlib-side callers.