This PR introduces support for electronic e-Resguardos for Uruguay, fully compliant with DGI regulations and integrated into the existing electronic invoicing flow via Uruware.

The implementation is based on the existing withholding framework from Ecuador, with references to Argentina’s approach, and includes the necessary adaptations to meet Uruguayan legal and functional requirements.

Key features included in this PR:

- Out-of-the-box availability: once the module is installed, users can create e-Resguardos without additional activation steps.
- Base configuration for withholdings:
  - Common withholding taxes (VAT and IRPF).
  - New field for DGI Withholding Code on taxes.
  - Configurable destination and default withholding accounts.
- Two main functional flows:
  - Creation of e-Resguardos from a single vendor bill.
  - Creation of e-Resguardos with multiple or no invoice references, including proper reference handling in XML depending on payment context.
- Automatic calculations of withheld amounts based on selected tax and base.
- XML generation and submission through the existing Uruware connection, including reception of validated XML (CAE) and PDF with electronic stamp.
- Compliance with the 10,000 UI threshold, enabling users to generate e-Resguardos when required by regulation.
- Storage and visualization of XML and PDF directly in Odoo, with printing support.
- Comprehensive testing coverage: single and multi-invoice cases, without reference, threshold logic, XML validation, and PDF rendering.

This PR lays the foundation for future extensions to additional e-Resguardo types while delivering a complete and compliant solution for the most common withholding scenarios in Uruguay.

Task: 4557347