backmp11: `state_machine` cannot be moved or copied

[chandryan]

The state_machine class has severe limitations regarding its copy and move operations:

Copy operations can only be applied without an event pool, because the underyling container basic_polymorphic is not copyable (regression introduced by basic_polymorphic).

Move operations have not been implememented yet.

Enable the class to be copyable and movable by making basic_polymorphic copyable and implementing the missing move operations.