Helper class for handling async poll requests. This class allows the response for an async poll
to be delayed until data arrives to return to the client or the specified wait interval elapses.
Wait timeouts are monitored by the FlexClientManager which contains a TimeoutManager
instance that is started and stopped during application bootstrap and shutdown. Managing timeouts
locally or statically isn't a good option because they lack a useful shutdown hook that's necessary
in order to close down the timeout manager cleanly.