Return a rejected promise instead of throwing

[jtojnar]

Otherwise it will mess up async clients.

While at it, fix developer tools (the old versions do not work on PHP 8 any more).

[j0k3r]

@jtojnar I've updated the CI, thanks for updating the code base 👍🏼
As we drop PHP < 7.4, I'll release 3.0 for it (or you might have more stuff to change?)

[jtojnar]

This looks nice for now. Cleaning up the types would be nice, opened #12. Another thing we could do is replace the obsolete php-http libraries with psr ones but that apparently requires psr/http-factory, which is currently incompatible with guzzlehttp/psr7.