cartopy: FeatureArtist is now a collection

[mathause]

• Closes #xxx
• Tests added
• Passes isort . && black . && flake8
• Fully documented, including whats-new.rst

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.71%. Comparing base (e74cb22) to head (e27c8b5).
Report is 14 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #525      +/-   ##
==========================================
- Coverage   99.79%   99.71%   -0.08%     
==========================================
  Files          17       17              
  Lines        1435     1407      -28     
==========================================
- Hits         1432     1403      -29     
- Misses          3        4       +1     

Flag	Coverage Δ
bare-minimum	?
min-all-deps	?
shapely_lt_2	?
unittests	99.71% <ø> (-0.08%)	⬇️

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[mathause]

The remaining failures are unrelated to cartopy - they seem a matplotlib - numpy v2 incompatability