/// A trait that defines the prefix string for a specific ID type.
///
/// This is typically implemented by zero-sized unit structs.
/// Defines a Prefix unit struct for use with [`crate::Puuid`].
///
/// # Example
/// ```rust
/// use puuid::prefix;
///
/// // Defines a public struct 'User' with prefix "user"
/// prefix!(pub User, "user");
///
/// // Defines a private struct 'Secret' with prefix "sk"
/// prefix!(Secret, "sk");
/// ```