Reverse the `.to_callable()` call

[clausmichele]

In some cases, to implement new processes, we need to get access to the original process graph (or at least the part related to that function call) inside of the called functions. Is it possible to do that with the current code structure?

So, starting from:
pg_callable = parsed_graph.to_callable(process_registry=process_registry)

being able to inspect the chain of calls inside pg_callable.