HttpRequest#executeAsync() may throw a RejectedExecutionException

[sotodel]

As described in the question and answer in this Stack Overflow post and this JDK issue, the ExecutorService returned by Executors.newSingleThreadExecutor can be finalized and shut down while still in use.

This may cause a RejectedExecutionException to be thrown while HttpRequest#executeAsync(Executor) is submitting its task.

I suggest changing HttpRequest#executeAsync() to use an ExecutorService returned by Executors#newFixedThreadPool(1), which isn't wrapped in a FinalizableDelegatingExecutorService.