First matching character from both ends

#[test]
fn test_example1() {
    let start = std::time::Instant::now();
    let val = Solution::first_matching_index("abcacbd".to_string());
    let expected = 1;
    log_result!(val == expected, "test_example1", start, &expected, &val);
    assert_eq!(val, expected);
}

#[test]
fn test_example2() {
    let start = std::time::Instant::now();
    let val = Solution::first_matching_index("abc".to_string());
    let expected = 1;
    log_result!(val == expected, "test_example2", start, &expected, &val);
    assert_eq!(val, expected);
}

#[test]
fn test_example3() {
    let start = std::time::Instant::now();
    let val = Solution::first_matching_index("abcdab".to_string());
    let expected = -1;
    log_result!(val == expected, "test_example3", start, &expected, &val);
    assert_eq!(val, expected);
}

#[test]
fn test_palindrome() {
    let start = std::time::Instant::now();
    let val = Solution::first_matching_index("abba".to_string());
    let expected = 0;
    log_result!(val == expected, "test_palindrome", start, &expected, &val);
    assert_eq!(val, expected);
}

#[test]
fn test_single_char() {
    let start = std::time::Instant::now();
    let val = Solution::first_matching_index("a".to_string());
    let expected = 0;
    log_result!(val == expected, "test_single_char", start, &expected, &val);
    assert_eq!(val, expected);
}