/// Caesar Cipher
///
/// Caesar's cipher shifts each letter by a fixed number of positions in the
/// alphabet. Letters wrap around when they pass the end of the alphabet.
///
/// # Examples
///
/// Basic usage:
/// ```
/// let result = algorithmz::string::caesar_cipher("Hello_World!",10);
/// assert_eq!(result, String::from("Rovvy_Gybvn!"));
/// ```