New xcube rule no-chunked-coords

[forman]

Closes #29

Checklist (strike out non-applicable):

• Changes documented in CHANGES.md
• Related issue exists and is referred to in the PR description and CHANGES.md
• Added docstrings and API docs for any new/modified user-facing classes and functions
• Changes/features documented in docs/*
• Unit-tests adapted/added for changes/features
• Test coverage remains or increases (target 100%)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.47%. Comparing base (4a79e95) to head (a1a67f8).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #32      +/-   ##
==========================================
+ Coverage   97.46%   97.47%   +0.01%     
==========================================
  Files          61       62       +1     
  Lines        2441     2459      +18     
  Branches      343      346       +3     
==========================================
+ Hits         2379     2397      +18     
  Misses         31       31              
  Partials       31       31              

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