Add way to detect if calling context is blocking or not

A user can use either our blocking (Cache#put) or non blocking (Cache#putAsync) API. We should be able to optimize our usage of blocking threads based on this. In the case that the user is using the blocking API, we can assume the thread is a blocking thread (even though we don't control it), which would allow us to not have to spawn additional threads to wait providing for less context switching and better resource utilization.

The main question is how do we detect such things. An idea is a thread local, command boolean, context flag etc.