Optimize: support pyswarm 1.0 return format

[Doresic]

pyswarm 1.0 changed pso to return an object with x and fun instead of the old (xopt, fopt) tuple.

This keeps support for both formats, so older pyswarm versions still work while CI can also use the new release.
I considered changing requirements to pyswarm >= 1.0.0, but it seems there is no more installation wheel for intel macs there anymore, so instead I decided to suggest keeping support for all versions.

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 84.26%. Comparing base (e528598) to head (f1a1c4c).

Files with missing lines	Patch %	Lines
pypesto/optimize/optimizer.py	75.00%	1 Missing ⚠️
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Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1717      +/-   ##
===========================================
+ Coverage    78.93%   84.26%   +5.33%     
===========================================
  Files          164      164              
  Lines        14642    14645       +3     
===========================================
+ Hits         11557    12341     +784     
+ Misses        3085     2304     -781     

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