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

[github-actions[bot]]

On 2022-06-09 @recmo wrote in f0f0ddb “Merge pull request #126 from recmo/redc”:

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

                    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);
                    let br = b.mul_mod(r, m);
                    // TODO: Test for larger (>= m) values of a, b.

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

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

From src/modular.rs:282