Steps to reproduce
------------------
1. Install l10n_ke_edi_oscu_pos.
2. Select the Kenyan company.
3. Enable eTIMS on the PoS.
4. Register the products inside a combo, but not the combo itself.
5. Sell the combo in the PoS.

Observation
-----------
We see a warning that the combo must be registered to eTIMS, and the order can't be validated.

What's happening
----------------
In the PoS a combo adds a 0 price parent line for the combo product, but the combo is not a real item to send to eTIMS, only the products inside it are, and (as per step 4) the combo is not registered.

`checkEtimsFields` sees the combo as not registered, so it raises the warning in `showUnregisteredProductsWarning` and blocks the payment in `validateOrder`.

Fix
---
In the backend, we skip sending the parent combo line to eTIMS, and on the frontend, we make the combo parent line not need eTIMS registration, so the warning and the block don't apply to it.

opw-6253306

Forward-Port-Of: odoo/enterprise#121205
Forward-Port-Of: odoo/enterprise#119362

### Issue:
When invoicing partial quantities from a sale order, more DDTs than necessary are linked to the invoice

Since `l10n_it_ddt_ids` is computed and not stored, the incorrect links persist until the remaining quantities are invoiced, at which point the extra DDTs are moved to the new invoice

This creates inconsistencies in the generated XML, which references DDTs not actually covered by the invoice

### Cause:
The quantity allocation loop only checked whether there was remaining `move_qty` to consume, but never checked whether the invoiced quantity (`inv[0]`) had already been fully consumed

As a result, once all invoiced quantity was allocated, the loop kept iterating and linking additional DDTs from the sale order

### Steps to reproduce:
- Install `l10n_it_stock_ddt` with demo data
- Switch to the IT company
- Create a Warehouse
- Create a Product (Invoicing Policy: Delivered Quantities)
- Create and confirm a Sale Order (qty: 5) for that product
- Validate 3 partial deliveries of qty 1, creating a backorder each time
- Create the invoice, set the quantity to 2 and confirm

Before the fix, 3 DDTs were linked instead of 2

opw-6294035

Forward-Port-Of: odoo/odoo#270235