Fix isless and update tests

[adrhill]

Closes #153.

• fix isless by adding additional method on AbstractFloat
• update Jacobian and Hessian tests

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.25%. Comparing base (8451650) to head (3dac86b).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #161      +/-   ##
==========================================
+ Coverage   85.39%   89.25%   +3.85%     
==========================================
  Files          37       37              
  Lines        1527     1517      -10     
==========================================
+ Hits         1304     1354      +50     
+ Misses        223      163      -60     

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