Combine zn.deps and zn.nodes

[PythonFZ]

The two implementations of zn.nodes and zn.deps seem to lead to a lot of confusion.
Would it improve or overcomplicate combining the two into one?

calc = ... # this won't have its run method called
with Project():
   sim(calc=calc) # zn.nodes

with Project():
   calc = ... # this will it's run method have called.
   sim(calc=calc) # zn.deps