Pico return references

[rbalicki2]

• Memoized functions can return references
• Memoized functions do not accept references as parameters, only DB can be a reference
  • we should always pass small, copiable objects (like names or IDs), not large objects that we worry about cloning

unchanged stuff:

• params should remain hash / WithSerializable
• GC should work as is? As in, we GC from the root query and (lower priority) GC the related derived nodes, so the last thing to be GC'd will be the "underlying truth", i.e. in get_first_item_in_selection_set -> get_selection_set -> get_entity -> parse_graphql_schema, we will GC from the left side, and all references point "to the right"