/// Atbash Cipher
///
/// Atbash cipher maps each letter of the alphabet to its reverse. The first letter 'a' maps to 'z', 'b' maps to 'y', and so on.
///
/// # Examples
///
/// Basic example:
/// ```
/// let result = algorithmz::string::atbash_cipher("abcdefghijklmno");
/// assert_eq!(result, "zyxwvutsrqponml".to_string());
/// ```