(doc/test) improve r1/r2/r3 rotation matrix

[ThibFrgsGmz]

• Improved docstrings: more detail and better rendering in the IDE (VSCode at least)
• Added some unit tests

[codecov]

Codecov Report

Patch coverage: 72.72% and project coverage change: +0.10 🎉

Comparison is base (2ee5225) 66.33% compared to head (9f254a5) 66.44%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #176      +/-   ##
==========================================
+ Coverage   66.33%   66.44%   +0.10%     
==========================================
  Files         127      127              
  Lines       32445    32466      +21     
==========================================
+ Hits        21524    21571      +47     
+ Misses      10921    10895      -26     

Impacted Files	Coverage Δ
src/utils.rs	56.98% <72.72%> (+5.59%)	⬆️

... and 5 files with indirect coverage changes

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