PEP517/PEP621 compatibility

What are the plans for migrating the build system from the `setup.py` to a build backend supporting PEP621 format? (biassed towards `scikit-build-core` of course )

Packaging wise there could be some issues to resolve:

• Fedora, Ubuntu, OpenSUSE, Arch, etc.: No issues, `scikit-build-core` is packaged and maintained properly
• PyPI, conda: No issues, natively supported
• spack: No issues, packaged
• homebrew: No issues, python packages are vendored
• RHEL: `scikit-build-core` is not part of the CentOS packages, and I don't think it will for similar issues that `hatchling` is not. However, I see that `pyside6` is actually packaged within CentOS [1]. Not sure why it is needed there, would need to do some research and discuss with EPEL folks if it is viable to be moved. `pyside6` is only in EPEL10, and `scikit-build-core` will be in EPEL10 as well.
• Debian: Both `pyside6` and `scikit-build-core` are only packaged on Debian Sid. Should be fine, afaict
• yocto: `scikit-build-core` support is still a WIP, but I guess `pyside6` support there is also not present?

Of course you can replace `scikit-build-core` with another supported build backend, but for CMake I don't think you have a better one. Did I miss any other distributions?

[1]: https://pkgs.org/search/?q=pyside
[2]: https://pkgs.org/search/?q=scikit-build-core