[FR] Support `.tar.zst` (zstandard-compressed tarball) source distribution formats

[lengau]

What's the problem this feature will solve?

Now that compression.zstd is included in Python 3.14, it would be really nice to be able to build zstd-compressed source files.

Describe the solution you'd like

When I run python setup.py sdist --formats=zsttar I would like to be able to to create a tarfile with zst compression if the Python executable I'm using supports it.

Alternative Solutions

Currently you can use --formats=tar and then compress it with zstandard afterwards, but that's a inconvenient.

Additional context

Several Linux distributions are moving to using zstandard for their packages, and other package managers such as brew accept zstandard-compressed source files.

Code of Conduct

• I agree to follow the PSF Code of Conduct

[abravalheri]

Hi, python setup.py sdist is a deprecated command in favour of other alternatives like python -m build.

This change is likely to require a packaging PEP and may have been discussed in https://discuss.python.org/c/packaging/14.