♻️(backend) rework factories

[kernicPanel]

Bug Report

There is something weird here about the ContractFactory...

Instead of

order = factories.OrderFactory(product=product, owner=owner, contract=factories.ContractFactory())

this will work

order = factories.OrderFactory(product=product, owner=owner)
factories.ContractFactory(order=order)

Indeed, the ContractFactory uses a SubFactory to generate its related order.
So with your statement, the Contract is generated before the order so another Order is created before and linked to the Contract ...

To resume what's wrong, here it is a statement that will return True :

order.contract.order != order

Originally posted by @jbpenrath in #489 (comment)