Maximum product of three numbers

#[test]
fn t1() {
    let s = std::time::Instant::now();
    let v = Solution::maximum_product(vec![1,2,3]);
    log_result!(v == 6, "t1", s, 6, v);
    assert_eq!(v, 6);
}

#[test]
fn t2() {
    let s = std::time::Instant::now();
    let v = Solution::maximum_product(vec![1,2,3,4]);
    log_result!(v == 24, "t2", s, 24, v);
    assert_eq!(v, 24);
}

#[test]
fn t3() {
    let s = std::time::Instant::now();
    let v = Solution::maximum_product(vec![-1,-2,-3]);
    log_result!(v == -6, "t3", s, -6, v);
    assert_eq!(v, -6);
}

#[test]
fn t4() {
    // two negatives + one large positive
    let s = std::time::Instant::now();
    let v = Solution::maximum_product(vec![-100,-98,1,2,3,99]);
    log_result!(v == 970200, "t4", s, 970200, v);
    assert_eq!(v, 970200);
}

#[test]
fn t5() {
    let s = std::time::Instant::now();
    let v = Solution::maximum_product(vec![-1, -2, 0, 1, 2]);
    log_result!(v == 4, "t5", s, 4, v);
    assert_eq!(v, 4);
}