Clearly the use of errgroup is flawed.
1) You can't pass in variables, so this is likely to race.
2) You can't get a set of errors, so this is a bad API.
For the second problem, it would be much more sane to return a multierr
or a list of errors. If there's no fix for the first, I think it should
be removed from the lib.
Resources can send "refresh" notifications along edges. These messages
are sent whenever the upstream (initiating vertex) changes state. When
the changed state propagates downstream, it will be paired with a
refresh flag which can be queried in the CheckApply method of that
resource.
Future work will include a stateful refresh tracking mechanism so that
if a refresh event is generated and not consumed, it will be saved
across an interrupt (shutdown) or a crash so that it can be re-applied
on the subsequent run. This is important because the unapplied refresh
is a form of hysteresis which needs to be tracked and remembered or we
won't be able to determine that the state is wrong!
Still to do:
* Update the autogrouping code to handle the edge notify properties!
* Actually finish the stateful bool code
