Multiple ZIP intervals for the same delivery method

This module extends the delivery method configuration so that one shipping method can cover many ZIP code intervals instead of a single prefix list.

On the delivery method form (Delivery methods), a new radio choice lets you pick how ZIP codes are matched: "Prefixes" (the standard behaviour) or "Ranges". When "Ranges" is selected, the standard prefix list is hidden and a new editable list called "ZIP codes" appears, where you enter a From and To value per line. Each line is automatically named "from - to".

When Odoo checks whether a delivery method is available for a customer address, it first applies the normal matching rules. If the method is set to "Ranges" and interval lines exist, the address is only accepted when the customer's ZIP code falls between the From and To values of at least one line. Otherwise the carrier is not offered.

Access rights are added for the new ZIP interval lines: salespeople, partner managers and stock users can read them, while sales and stock managers can also create, edit and delete them.

The module touches the delivery.carrier model and adds a new delivery.carrier.zip model, and it modifies the delivery method form view.