Implement PEP 625 (naming of sdists and projects)

[philthompson10]

PEP 625 and the current wheel spec. specify that project names and sdists should use lower case names. Implementing this will change the names of sdists and wheels which may cause problems for external tooling and so should probably be done as part of a feature release.

setuptools v69.3.0 implemented this support which impacts the names of the generated sip module sdists, but does not impact the names of the corresponding wheels (which is determined by the project name set by sip-module).

The project name in the generated sip modules' pyproject.toml files should be lower case and lower case should be used in the name of any generated sdist and wheel files.

[philthompson10]

Ultimately the specification of the format of a distribution name (and therefore sdist and wheel file names) is in the Escaping and Unicode section of the binary distribution section of the Python Packaging User Guide. Although it specifies the use of lower case characters it also states that tools consuming wheels must also be prepared to accept upper case characters.

We therefore choose the leave the current implementation as it is to avoid potential compatibility problems for existing projects. It is up to project authors to implement distribution names as they see fit.

[philthompson10]

PyPI is now sending emails warning that in future sdists must conform to PEP 625.

[philthompson10]

sdists now have lower case file names but the project names have been left untouched. Hopefully this is enough to satisfy PyPI.