Implement slight pause on engine stop

[qdot]

Via sentry, we've seen instances of users hammering the start/stop engine button while crash loops are happening. Apparently we can send engine stopped events before all of the native tasks have cleared out, which causes some really weird errors. Put in a slight delay after a crash happens or engine is stopped (like 500ms) to give the native runtime some room to clean up for now. This can be removed once we have a guarantee in place that we'll have finished out all native tasks before sending the engine stopped message.