Fix to provide php v8.1 compatibility

[coresh]

Provided: Avoid deprecation User Deprecated: Method "Countable::count()" might add "int" as a native return type declaration in the future. Do the same in implementation "Ratchet\RFC6455\Messaging\Message" now to avoid errors or add an explicit @return annotation to suppress this message.

[3kbest]

Please merge 👍