.really_destroy! should not destroy has_many :through records

[atd]

Despite of counter intuitive, Rails API states that has_many :through records must not be destroyed, but their associations https://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html#method-i-has_many

If using with the :through option, the association on the join model must be a belongs_to, and the records which get deleted are the join records, rather than the associated records.

paranoia should have the same behavior

Fixes #466

[mathieujobin]

I see that current tests pass https://github.com/rubysherpas/paranoia/actions/runs/2026327334

But I would like to see a test case added for this and few more people advocating for this to be merged before taking side.