Patch vendored packaging library to support `--disable-gil` (PEP 703) builds

[colesbury]

What's the problem this feature will solve?

The current version of pip does not support the free-threaded builds of CPython 3.13 due to using an older version of the packaging library. Currently, pip 24.0 will install incompatible stable ABI wheels and also refuse to install compatible wheels in the free-threaded build.

#12300 upgrades the vendored packaging library, but the PR still has unresolved issues that are unrelated to support for the free-threaded CPython build.

Describe the solution you'd like

As a stopgap measure, let's patch the vendored packaging library with the changes from pypa/packaging#728 in order to support the free-threaded build.

This decouples support for free-threaded CPython and removal of legacy version specifiers. Supporting free-threaded CPython is fairly straightforward, while the removal of legacy versions and version specifiers is complex.

Alternative Solutions

Alternatively, we can wait for the remaining issues in #12300 to be addressed.

Additional context

The May 7 beta release of Python 3.13 is coming up soon. If possible, I'd really like to have a version of pip that works with the free-threaded build before then.

Code of Conduct

• I agree to follow the PSF Code of Conduct.

[pradyunsg]

Closing this out since #12300 has merged.