This adds the ability to wait with a timeout for CheckApply happenings
in a resource. This helps avoid unnecessary long sleeping and timing
guesses. This also adds a cleanup function to run at the end.
The engine core had some unfortunate bugs that were the result of some
early design errors when I wasn't as familiar with channels. I've
finally rewritten most of the bad parts, and I think it's much more
logical and stable now.
This also simplifies the resource API, since more of the work is done
completely in the engine, and hidden from view.
Lastly, this adds a few new metaparameters and associated code.
There are still some open problems left to solve, but hopefully this
brings us one step closer.
This adds a simulated engine that can run and test single resources. It
can't test all aspects and features that the engine supports, but is
probably pretty decent for testing the actual CheckApply and Watch
semantics. Be warned that it actually applies changes on your machine,
so please don't write tests that make undesirable changes.
