Add packaging as a core dependency of MDAnalysis

[IAlibay]

Follow-up from #3527

Changes made in this Pull Request:

• Adds packaging as a core dep of MDAnalysis (this was added in Chemfiles updates #3499 but I messed up on adding it in properly sorry 😞 )

PR Checklist

• Tests?
• Docs? - userguide needs updating
• CHANGELOG updated?
• Issue raised/referenced?

[codecov]

Codecov Report

Merging #3549 (5c386d6) into develop (acd929f) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop    #3549   +/-   ##
========================================
  Coverage    94.11%   94.11%           
========================================
  Files          190      190           
  Lines        24642    24642           
  Branches      3309     3309           
========================================
  Hits         23192    23192           
  Misses        1404     1404           
  Partials        46       46           

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[IAlibay]

Lots of "TestOpenMMBasicSimulationReader" failures on MacOS, need to investigate in the morning.

[lilyminium]

LGTM, thanks!

[IAlibay]

Thanks @lilyminium - I'll fix CI in the next PR so we can be green prior to release.