wrapThenCallback example

    private GuzzlePromiseInterface $promise;

    public function __construct(GuzzlePromiseInterface $promise)
    {
        $this->promise = $promise;
    }

    public function then(callable $onFulfilled = null, callable $onRejected = null): self
    {
        return new self($this->promise->then(
            $this->wrapThenCallback($onFulfilled),
            $this->wrapThenCallback($onRejected)
        ));
    }

    public function cancel(): void
    {
        $this->promise->cancel();
    }

    public function getState(): string
    {