changed: f̂ now internally handle the operating points

[franckgaga]

This is simpler since the users of the function, that is PredictiveController and StateEstimator objects, no longer need to add f̂op subtract x̂op after calling f̂

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.56%. Comparing base (ffc3bda) to head (11d4f9e).
⚠️ Report is 9 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #241   +/-   ##
=======================================
  Coverage   98.56%   98.56%           
=======================================
  Files          26       26           
  Lines        4375     4379    +4     
=======================================
+ Hits         4312     4316    +4     
  Misses         63       63           

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