Product packaging calculator packaging level

This module is a small bridge between the packaging calculator and the packaging level features. It does not add new screens or menus; it changes the text that Odoo shows when a product quantity is broken down by packaging.

• When a packaging has a packaging level defined, the quantity display uses the level's code (or another chosen field) instead of the packaging name. For example, "1 Pallet, 2 Big Box, 7 Box, 10 Units" becomes "1PL, 2TU, 7CU, 10 Units".
• The display can be compact (no space between the number and the code, like "1PL") or spaced ("1 PL"), controlled by context.
• The field used for the level label can be changed through context; by default it is the code.
• If a packaging has no packaging level, the previous behaviour is kept.

Technically it extends product.product and the abstract mixin product.qty_by_packaging.mixin, overriding the methods that build the packaging name and the quantity-by-packaging string, and re-declaring the computed display field so it reacts to language and the new context options. No new models, fields, menus, or scheduled actions are added.