Add PHP 8.4 compatibility

[chrisdeeming]

Deprecated
: JoyPixels\Client::__construct(): Implicitly marking parameter $ruleset as nullable is deprecated, the explicit nullable type must be used instead in
/Users/chrisdeeming/Herd/24x/src/vendor/joypixels/emoji-toolkit/lib/php/src/Client.php
on line
29

I'll report back any other issues I find here (if any) but this one is a simple change at least:

public function __construct(RulesetInterface $ruleset = null)

Becomes:

public function __construct(RulesetInterface? $ruleset)

This will require the library to be updated to support at least PHP 7.1.

Still supporting PHP 5.3 in 2024 is, frankly, unnecessary!