Add support for PEP 794

[jenshnielsen]

PEP 794 (Accepted 05-Sep-2025) adds fields project.import-names and project.import-namespaces, Currently validate-pyproject rejects these fields with

Invalid file: pyproject.toml
[ERROR] `project` must not contain {'import-names', 'import-namespaces'} properties

I noticed this since setuptools uses this project for validation and currently rejects these fields at build time.

[henryiii]

#271 added this, though it’s not in a release yet.

[henryiii]

Also, until we release packaging, not much is going to support this. (PyPI, Twine, etc) so there’s not much point in making a wheel yet with this metadata if you can’t upload it.

[jenshnielsen]

@henryiii Thanks. I don't know how I overlooked this when searching.