Handle transient VIES faults gracefully

[eason4kim-rocket]

Summary

• convert known transient VIES SOAP faults into a field-level ValidationError with the vies_unavailable code
• keep unknown SOAP faults visible instead of swallowing them
• cover both direct validation and the Django model-form path

When VIES returns MS_MAX_CONCURRENT_REQ (or another documented temporary availability fault), the form now reports that VIES is temporarily unavailable instead of allowing the Zeep fault to become a server error. The VAT number is not described as invalid.

Tests

• uv run pytest — 39 passed
• uvx ruff check vies/types.py tests/test_types.py tests/test_widgets.py
• uvx ruff format --check vies/types.py tests/test_types.py tests/test_widgets.py

Fixes #314.

[codingjoe]

Wonderful start!

The current code is a little old, and I am ashamed of it. While you are at it, can you improve the logging messages? Python has a native way to include exceptions (exc_info=True). Log messages should provide additional context and don't need to include the exception.

I'd be much simpler if we'd get explicit exceptions per failure, not just Fault, but hey 🤷

Thanks
-joe

[codingjoe]

Let's use some of Python's internal magic.

Suggested change

	logger.warning("Transient VIES fault: %s", e.message)
	logger.warning("Transient VIES fault: %r", e, exc_info=True)

[codingjoe]

Suggested change

	logger.exception(e)
	logger.exception("Unexpected error")

[codingjoe]

It might be nice to use match..case here and provide proper messages (or at least log messages) per expected failure.

E.G. a timeout should be logged as an error, not a warning, since its the cause could be inside your own infrastructure.