HotRod Java client should allow virtual threads for callbacks

Currently we invoke a callback for the client on the netty event loop thread. This can cause issues if the user uses a blocking call and can even completely stall the thread if they invoke a blocking client operation to the server which would require the same event loop thread to send.

The question becomes do we always use a virtual thread when using JDK 21+ or should it be optional based on a property. Feeling currently is we should always enable it.