ENH: Consistency check of user-provided `bg_id`

[MImmesberger]

Check whether the bg_id is sensible if provided by the user.

For example, we can check whether

• there are at most 2 adults in one BG (not counting their children)
• children are only in the same BG if their parents are part of it as well
• individuals with the same bg_id don't have different wthh_ids
• individuals with the same sn_id, ehe_id or eg_id have the same bg_id

[MImmesberger]

Quick question regarding this: I planned to check the IDs before the DAG is created. But to test the specification of bg_id I either need to have the outcome of some tax functions available (e.g. kindergeld_anspruch). Or I test the specification via the inputs of p_id_elternteil, p_id_ehepartner, etc. which makes them mandatory inputs. Do you have any preference? @hmgaudecker

[hmgaudecker]

Yes, those p_ids should be mandatory.