Remove Ipopt as dependency

[blegat]

It's only a dependency of the tests

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.77%. Comparing base (f6d8fbd) to head (ca2e2e7).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #13   +/-   ##
=======================================
  Coverage   72.77%   72.77%           
=======================================
  Files           5        5           
  Lines         202      202           
=======================================
  Hits          147      147           
  Misses         55       55           

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