Look into removing firehed/security as a hard dependency

[Firehed]

Since the #[SensitiveParameter] attribute has native support in PHP 8.2, one of the main reasons for importing and relying on this library has become obsolete (currently-supported versions of PHP notwithstanding).

In practice, I've found a combination of __debugInfo() (#13) and sensible setup makes this mostly into added API complexity. Removing it as a requirement is generally beneficial as it reduces dependency surface area and is one less thing to deal with when dealing with language version updates. If it can be moved to suggest and left optional, I think that's a net win.