Events do not process when an operator is under high load

[pschafhalter]

When an operator is under high load (i.e. messages are coming in at a very high rate), events are only inserted into the lattice and not removed/processed until the rate of incoming messages decreases.

This may be due to a prioritization issue related to how the operator executor interacts with Rust futures or the underlying runtime since the threads responsible for running events should access the lattice at the same time as the thread inserting events.