Simplify push event queue impl

[robambalu]

The CSP Engine doesnt need to deal with the lock free queue with optional blocking, it's never really going to be used in non-blocking / busy looping mode. We can replace it with a much simpler queue + mutex/condvar. No need for lockfree queues here, which also complicates how we (optionally) wait for data but may not process the data if timers are ready to fire