Update the logic to adapt for the new UK VAT endpoint

[CrochetFeve0251]

Description

Fixes #149

Fix the bug by using the new API from gov.uk where it returns a 404.

For that we had to upgrade the library to use the version 2 of the API with Oauth authentification.

Type of change

• New feature (non-breaking change which adds functionality).
• Bug fix (non-breaking change which fixes an issue).
• Enhancement (non-breaking change which improves an existing functionality).
• Breaking change (fix or feature that would cause existing functionality to not work as before).
• Sub-task of #(issue number)
• Chore
• Release

Detailed scenario

What was tested

Describe the scenarios that you tested, and specify if it is automated or manual. For manual scenarios, provide a screenshot of the results.

The new code was tested manually on the testing env using this script:

from pyvat.registries import HMRCRegistry

r = HMRCRegistry()

res =  r.check_vat_number('553557881', 'GB', True)

print(res.is_valid)

Then I used the keys to test both a valid VAT number and an invalid one in production and testing.

How to test

Describe how the PR can be tested so that the validator can be autonomous: environment, dependencies, specific setup, steps to perform, API requests, etc.

Use the script and set the env variables:
PYVAT_UK_CLIENT_ID=
PYVAT_UK_CLIENT_SECRET=

You need to find a client in WP Rocket with a valid VAT and use a fake VAT as such as 123456789 to make sure both cases are covered.

Technical description

Documentation

Explain how this code works. Diagrams & drawings are welcome.

New dependencies

List any new dependencies that are required for this change.

Risks

List possible performance & security issues or risks, and explain how they have been mitigated.

Mandatory Checklist

Code validation

• I validated all the Acceptance Criteria. If possible, provide screenshots or videos.
• I triggered all changed lines of code at least once without new errors/warnings/notices.
• I implemented built-in tests to cover the new/changed code.

Code style

• I wrote a self-explanatory code about what it does.
• I protected entry points against unexpected inputs.
• I did not introduce unnecessary complexity.
• Output messages (errors, notices, logs) are explicit enough for users to understand the issue and are actionnable.

Unticked items justification

This is a library with few tests and a fork.
If some mandatory items are not relevant, explain why in this section.

Additional Checks

• In the case of complex code, I wrote comments to explain it.
• When possible, I prepared ways to observe the implemented system (logs, data, etc.).
• I added error handling logic when using functions that could throw errors (HTTP/API request, filesystem, etc.)

[Copilot]

PR Overview

This PR fixes the bug related to the new HMRC VAT validation endpoint and updates naming conventions from “United Kingdom” to “Great Britain”.

• Updated HMRCRegistry to use separate base URLs and added explicit authentication logic with OAuth.
• Renamed “GB” comments and docstrings in both the country definitions and VAT rules to reflect the updated naming.
• Reordered instantiation of HMRCRegistry in init.py for improved clarity.

Reviewed Changes

File	Description
pyvat/registries.py	Updated HMRCRegistry logic for new API endpoints and OAuth flow.
pyvat/countries.py	Updated comment for 'GB' to “Great Britain”.
pyvat/vat_rules.py	Updated VAT rules docstring to use “Great Britain” instead of “United Kingdom”.
pyvat/init.py	Reordered instantiation of HMRCRegistry.

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

[Copilot]

[nitpick] Consider using a URL joining function (such as urllib.parse.urljoin) for more robust URL construction and to avoid potential issues with missing or extra slashes.

Suggested change

	url = "{0}/organisations/vat/check-vat-number/lookup/".format(base_url)
	headers = self._authentication_headers()
	response = requests.get(
	url + vat_number,
	url = urljoin(base_url, "/organisations/vat/check-vat-number/lookup/")
	headers = self._authentication_headers()
	response = requests.get(
	urljoin(url, vat_number),

[nicomollet]

Approved (FYI this branch is on your personal GH account)

Can this be deployed somehow to Monies staging?
Can we change Monies requirements to use this branch https://github.com/wp-media/monies/blob/develop/requirements.txt

[CrochetFeve0251]

@nicomollet we need to add the env secrets into the k8 namespaces first let me handle that