Never aggregate lines (split_on_line).
Find proper invoice (first_causality_on_delivery).
Avoid setting not needed categories (specialise and causality).

Also fixup naming.

Builder is used to create one and only one invoice.

Also declare other tests and avoid code duplication.

There are some tricks around transaction which lead to decision to defer the
expand. Instead of complexing test code and add this tricks it is easier to
use public updateSimulation.

More things were destroyed in 7cec0b75

Causality is not set on SPL, as there is no (for now) Movement Group supporting
Hosting Subscription as causality from Root Applied Rule.