An asynchronous execution interceptor for methods returning {@link Future}. Because asynchronous invocations necessarily run in a concurrent thread, any thread context setup interceptors should run
after this interceptor to prevent that context from becoming lost. This interceptor should be associated with the client interceptor stack.
Cancellation notification is accomplished via the {@link CancellationFlag} private data attachment. This interceptorwill create and attach a new cancellation flag, which will be set to {@code true} if the request was cancelled.
@author David M. Lloyd