Add more test cases for diamond and rectangle shapes

[stefmolin]

• Make line tests easier to debug
• Update diamond test cases
• Update rectangle test cases

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.80%. Comparing base (82c8ba6) to head (badfff3).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #292   +/-   ##
=======================================
  Coverage   98.80%   98.80%           
=======================================
  Files          84       84           
  Lines        2097     2098    +1     
  Branches      121      121           
=======================================
+ Hits         2072     2073    +1     
  Misses         24       24           
  Partials        1        1           

Files with missing lines	Coverage Δ
tests/shapes/lines/bases.py	100.00% <100.00%> (ø)
tests/shapes/lines/test_diamond.py	100.00% <100.00%> (ø)
tests/shapes/lines/test_rectangle.py	100.00% <100.00%> (ø)