Partner Multi Relation Archive Propagate

## Partner Multi Relation Archive Propagate

This module extends the behaviour of partner_archive_propagate to also
propagate archiving and unarchiving **via partner_multi_relation
relations**.

When a company is archived:

- all related partners linked through relation types with
  `propagate_archive = True` are considered for propagation;
- related partners without active users are archived and marked with
  `propagated_from_id` pointing to the company;
- related partners linked to active users are skipped and listed in a
  message on the company.

When the company is unarchived, all partners that were archived because
of it – whether through the partner hierarchy or through multi-relations
– are restored automatically by the core partner_archive_propagate
logic.

Non-company partners do not propagate via this module, even if they are
involved in relations with `propagate_archive = True`.