modular: Test for larger (>= m) values of a, b.

[github-actions]

On 2024-12-16 @prestwich wrote in e657576 “Merge pull request #402 from recmo/recmo/montgomery”:

Test for larger (>= m) values of a, b.

                if let Some(inv) = U64::from(m.as_limbs()[0]).inv_ring() {
                    let inv = (-inv).as_limbs()[0];

                    let r = U::from(2).pow_mod(U::from(64 * LIMBS), m);
                    let ar = a.mul_mod(r, m);
                    // TODO: Test for larger (>= m) values of a, b.

                    let expected = a.mul_mod(a, m).mul_mod(r, m);

                    assert_eq!(ar.square_redc(m, inv), expected);
                }

From src/modular.rs:326