Allows for deferred execution of logic, useful when trying to get multiple components to coordinate behavior. A
component may add a command to be executed "at the end of the heartbeat". The classic example of
this is a Label and the field it labels; since we don't know which order the two will render, we can't tell if the
field's id is correct until after both have rendered.
The Heartbeat is injected into components via the Environmental annotation.