Increase maxfun for cobyla

[andreasnoack]

And make maxfun conditional on the solver since cobyla needs many more function evaluations than the other solvers.

The current failures on macos and arm are because the COBYLA fits slightly exceed the number of allowed function evaluations (6000). I guess slight rounding differences could cause COBYLA to take some extra and costly steps.

Closes #34

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.66%. Comparing base (6bc54d7) to head (cd37f02).
Report is 23 commits behind head on main.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main      #45      +/-   ##
==========================================
- Coverage   87.50%   85.66%   -1.84%     
==========================================
  Files           4        4              
  Lines         320      300      -20     
==========================================
- Hits          280      257      -23     
- Misses         40       43       +3     

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