Fix invalid parent cache invalidation

A relation embedded in 2 parents would only clear the cache in one of them.

Embedding twice an object would override `expire_parent_cache` and only the latest embedding parent would be cleared on child change.

This PR keeps these callback with unique names to prevent that clash.

@dylanahsmith What do you think?
Because of `test_cache_invalidation_expire_properly_if_child_is_embed_in_multiple_parents` that does not do it like other tests.