fix: accept swiss VAT IDs from customers

[barredterra]

This pull request adds support for validating and normalizing Swiss VAT IDs (UIDs) within the European e-invoice system. The main changes include implementing Swiss VAT ID validation logic, integrating this logic into the sales invoice workflow, and adding corresponding unit tests.

Swiss VAT ID validation and normalization:

• Added normalize_swiss_vat_id and is_valid_swiss_vat_id functions to eu_einvoice/switzerland.py for cleaning and validating Swiss VAT IDs according to official rules, including checksum verification.
• Integrated Swiss VAT ID validation into the _set_buyer_tax_id method in sales_invoice.py, so that Swiss VAT IDs are recognized and normalized before further processing.
• Imported the new Swiss VAT ID utilities in sales_invoice.py to enable their use.

Testing:

• Added unit tests in test_switzerland.py to verify the correctness of the Swiss VAT ID validation logic, including both valid and invalid cases.

[HenningWendtland]

Tested and it worked for me after applying the suggested change removing the suffixes. Checked also with the debugger that this was the problem.

[HenningWendtland]

Also the test file is missing a "." in the name, so it does not run

[barredterra]

@Mergifyio backport version-16-hotfix version-15-hotfix

[mergify]

backport version-16-hotfix version-15-hotfix

✅ Backports have been created

Details

• #234 fix: accept swiss VAT IDs from customers (backport #233) has been created for branch version-16-hotfix
• #235 fix: accept swiss VAT IDs from customers (backport #233) has been created for branch version-15-hotfix