Performance improvements

[mcgalcode]

Improves the speed of neighborhood building for some simple cases and adds tests.

[codecov]

Codecov Report

❌ Patch coverage is 86.52482% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.68%. Comparing base (1ca08f0) to head (e5b01fc).
⚠️ Report is 7 commits behind head on master.

Files with missing lines	Patch %	Lines
.../pylattica/structures/square_grid/neighborhoods.py	67.30%	15 Missing and 2 partials ⚠️
src/pylattica/structures/square_grid/grid_setup.py	75.00%	1 Missing ⚠️
...c/pylattica/visualization/square_grid_artist_3D.py	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #23      +/-   ##
==========================================
+ Coverage   94.12%   94.68%   +0.55%     
==========================================
  Files          48       48              
  Lines        1431     1525      +94     
  Branches      177      188      +11     
==========================================
+ Hits         1347     1444      +97     
+ Misses         65       60       -5     
- Partials       19       21       +2     

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