PHP 8.4 Deprecations

[mbabker]

With PHP 8.4 deprecating support for implicit nullable parameters, there are deprecation messages emitted from this package, including:

• Ratchet\RFC6455\Messaging\MessageBuffer::__construct(): Implicitly marking parameter $permessageDeflateOptions as nullable is deprecated, the explicit nullable type must be used instead

These should all be fixable on the v0.4 branch as it has raised the required PHP version to 7.4, but they are unfixable on master since it still supports PHP 5.4.