BLD, MAINT: Add `packaging.version` to the repo

[jbarnoud]

Following the discussion in #3527 (comment) we should provide packaging.version to the repo to avoid an issue with dependencies.

The file to vendor can be found here: https://github.com/pypa/packaging/blob/main/packaging/version.py

From the top of my head, here are the steps to follow:

• Copy the file to the repo
• Adapt the file's license header to tell about its origin
• Adapt our LICENSE file to mention packaging
• Make sure we use our version of the file in setup.py
• Make sure we use our version of the file everywhere else (including

  mdanalysis/package/MDAnalysis/coordinates/chemfiles.py

  Line 84 in 6b3a160

  from packaging.version import Version

  )

This issue is a follow up to #3527 and is related to @tylerjereddy's #3526

[markvrma]

I would like to work on this.

[orbeckst]

Hi @markvrma , please just work on the issue. We don't reserve issues, we simply review the first PR that comes in and references the issue. You get priority by showing work.