Get rid of parent backlinking

[mstechly]

Right now each "subobject" of Routine (e.g.: Connection, Port, children) have a link to their parent.
This is an artifact of the old implementation and causes a lot of issues: makes serialization more complicated, might lead to very hard to trace issues with pydantic, etc.

Getting rid of those backlinks would make Routine structure much simpler, though introducing this change might be non-trivial, as compilation depends on those backlinks to parents.

CC: @dexter2206