Use reactphp/async instead of clue/reactphp-block

[dinooo13]

See https://github.com/reactphp/async

Ref: clue/reactphp-block#67, clue/reactphp-block#68, reactphp/http#464 and clue/reactphp-mq#34

[SimonFrings]

@dinooo13 thanks for opening this PR 👍

This project uses the StreamSelectLoop instead of the default loop inside the test suite which is why switching them results in failing tests. This also means we can't switch from clue/reactphp-block to reactphp/async without adjusting this API first, because the React\Async\await() function doesn't accept a loop parameter.

@clue in I will look into switching to the default loop in another pull request, let's keep this open until this problem is fixed.

[dinooo13]

Ahh I was scratching my head what I have broken switching to the async package 😆