💡 Packing and flattening graph chunks

[liamhuber]

It would be nice to be able to take a subset of workflow nodes and package them automatically into a macro, like wf.package(wf.foo, wf.bar, wf.baz, inputs_map={"foo__finp": "widgets"}) or similar.

By the same token, it would be nice to be able to take a macro and unpack it so that its nodes belong directly to the macro's parent, e.g.

wf.nodes.labels 
>>> ["my_macro", "foo"]
wf.my_macro.nodes.labels
>>> ["a", "b", "c"]
wf.my_macro.flatten()
wf.nodes.labels
>>> ["a", "b", "c", "foo"]