retry option error: function true.wait_for/2 is undefined (module true is not available)

[qgadrian]

hello!

There is a bug in the current code for the retry options.
Currently, the retry option is typed in the %Opts{} struct as a boolean | module, but this fails when the value is a boolean (see the bug in this line).

Can you please fix it?
Otherwise, I can create a PR to get it fixed but before spending time on it I will need to know your idea for this retry option... is the boolean type deprecated? which default value should be preferred?

My initial approach would be something like (disclaimer, this code won't work it's just to get the idea)

  defp do_retry(result, request, opts) do
    attempt = Map.get(request.private, :attempt, 1)

    max_attempts = Keyword.get(opts.retry_opts, :max_attempts, 3)

    if max_attempts >= attempt do
      seconds_to_wait = seconds_to_wait(opts)

      :timer.sleep(seconds_to_wait)

      request
      |> Map.put(:private, Map.put(request.private, :attempt, attempt + 1))
      |> do_send(opts)
    else
      {:error, result}
    end
  end

  defp seconds_to_wait(retry: retry) when is_boolean(retry) do
    @whatever_default_wait
  end

  defp seconds_to_wait(retry: retry) when is_module(retry) do
    opts.wait_for(request, opts)
  end