fix for #158

[tjlane]

This PR ensures that Map.copy() propagates through and copies the .spacegroup and .cell attributes as well.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.89%. Comparing base (87faeca) to head (e6fcdc8).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #161      +/-   ##
==========================================
+ Coverage   94.87%   94.89%   +0.02%     
==========================================
  Files          16       16              
  Lines        1034     1039       +5     
==========================================
+ Hits          981      986       +5     
  Misses         53       53              

Flag	Coverage Δ
unittests	94.89% <100.00%> (+0.02%)	⬆️

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