`playground/cm31_ntt/src/cm31`: figure out why it doesn't work when

On 2025-11-05 in ac42e37 “Merge pull request #227 from worldfnd/sl/duplicate-witness”:

figure out why it doesn't work when
v equals CF { a: RF { val: 53cd1db6 }, b: RF { val: 5ac2fbb3 } }

        }
    }

    #[test]
    fn test_sqrt() {
        // TODO: figure out why it doesn't work when
        // v equals CF { a: RF { val: 53cd1db6 }, b: RF { val: 5ac2fbb3 } }
        let mut rng = ChaCha8Rng::seed_from_u64(1);
        let v: CF = rng.r#gen();
        let v = v.reduce();
        let v2 = (v * v).reduce();
        let s = v2.try_sqrt().unwrap();

From playground/cm31_ntt/src/cm31.rs:504

Start in playground/cm31_ntt/src/cm31.rs at the test_sqrt test and reproduce the seeded value shown in the issue. Trace the reduced CF value through multiplication and try_sqrt, then identify the cause of the failure. Done means the cause is explained and the behavior is covered by a passing regression test.