Add support for SpatGraticule

[dieghernan]

Close #155

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 99.60%. Comparing base (dd5e14e) to head (9404f4c).
Report is 3 commits behind head on main.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
R/fortify-Spat.R	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #158      +/-   ##
==========================================
- Coverage   99.63%   99.60%   -0.04%     
==========================================
  Files          50       50              
  Lines        3299     3300       +1     
==========================================
  Hits         3287     3287              
- Misses         12       13       +1     

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