refactor: php 8.4 - Deprecate implicitly nullable parameter types

[yuliyan-m]

This resolves deprecation warnings in the Ahc\Jwt\JWT class and ensures compatibility with PHP 8.4.

Deprecation Messages:

Deprecated: Ahc\Jwt\JWT::__construct(): Implicitly marking parameter $pass as nullable is deprecated, the explicit nullable type must be used instead at ..../vendor/adhocore/jwt/src/JWT.php:82

Deprecated: Ahc\Jwt\JWT::setTestTimestamp(): Implicitly marking parameter $timestamp as nullable is deprecated, the explicit nullable type must be used instead at ..../vendor/adhocore/jwt/src/JWT.php:182