Fixes etc

[gaelforget]

• allow modular choice of tests
• split test suite into separate files
• remove the MATLAB-style trailing semicolons
• fix EkmanTrsp calculation (stencil bug)
• fix untested option, add test, streamline variable names
• fix untested option, add test, streamline variable names
• remove export of undefined vars
• replace alias with similar

ps. assisted by claude sonnet

[codecov]

Codecov Report

❌ Patch coverage is 97.17742% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.40%. Comparing base (3dbc2ea) to head (d306589).

Files with missing lines	Patch %	Lines
src/Interpolation.jl	90.00%	4 Missing ⚠️
src/exchanges/CubeSphere.jl	97.05%	1 Missing ⚠️
src/grids/simple.jl	85.71%	1 Missing ⚠️
src/types/gcmarray.jl	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #223      +/-   ##
==========================================
+ Coverage   87.33%   87.40%   +0.06%     
==========================================
  Files          37       37              
  Lines        3428     3430       +2     
==========================================
+ Hits         2994     2998       +4     
+ Misses        434      432       -2     

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