Add mutex around step callback

[eeberhard]

After discoveries in https://github.com/aica-technology/stag/issues/7, there is a chance that the DSE state event handler unloads a component in one thread while the component step function is being handled in another thread. This race condition can cause memory issues and crashes.

Adding a mutex around the component step callback and the destructor could safeguard this race condition in a general way.

[domire8]

Reopening this, since we need to revert the revert commit once we are ready for a breaking 5.0.0 version