feat: Improve GeneticAlgorithm and add MAPElites

[engintoklu]

This pull request aims to improve the API related to genetic algorithm and its operators. The improvements are as follows:

• Added the class GeneticAlgorithm. The class SteadyStateGA remains, but is now an alias to GeneticAlgorithm.
• Added the boolean keyword argument elitist to GeneticAlgorithm. When set as False, the genetic algorithm will adopt a generational behavior, where the best-performing children always replace the worst-performing parents.
• Generalized the OnePointCrossOver operator to MultiPointCrossOver where the number of points is configurable. OnePointCrossOver remains as an alias with the number of points fixed as 1. Another alias is TwoPointCrossOver.
• Added the operator PolynomialMutation.
• Added the keyword argument operators to GeneticAlgorithm as the recommended way to to specify which operators are to be applied on the population at each generation.
• Added the MAPElites algorithm which, similar to GeneticAlgorithm, allows one to define the operators to be applied at each generation via the keyword argument operators.

Co-authored-by: Nihat Engin Toklu engin@nnaisense.com Co-authored-by: Pawel Liskowski pawel@nnaisense.com

[codecov-commenter]

Codecov Report

Merging #44 (0f35c54) into master (b92d9bb) will increase coverage by 0.71%. The diff coverage is 78.14%.

@@            Coverage Diff             @@
##           master      #44      +/-   ##
==========================================
+ Coverage   77.05%   77.77%   +0.71%     
==========================================
  Files          47       49       +2     
  Lines        6533     7319     +786     
==========================================
+ Hits         5034     5692     +658     
- Misses       1499     1627     +128     

Impacted Files	Coverage Δ
src/evotorch/core.py	74.48% <0.00%> (+0.84%)	:arrow_up:
src/evotorch/algorithms/ga.py	66.85% <57.14%> (+3.63%)	:arrow_up:
src/evotorch/tools/structures.py	79.50% <79.50%> (ø)
src/evotorch/algorithms/mapelites.py	83.69% <83.69%> (ø)
src/evotorch/tools/misc.py	86.36% <90.00%> (+0.09%)	:arrow_up:
src/evotorch/operators/real.py	93.00% <91.93%> (+11.39%)	:arrow_up:
src/evotorch/algorithms/__init__.py	100.00% <100.00%> (ø)
src/evotorch/operators/__init__.py	100.00% <100.00%> (ø)
src/evotorch/tools/__init__.py	100.00% <100.00%> (ø)
... and 3 more

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[NaturalGradient]

I've gone through the code and I'm generally happy. My only request is that maybe we can add an example that uses MAPElites? Although this could be added in a separate PR, I would appreciate a 'sensible use case' of the algorithm to play around with + verify it @engintoklu @pliskowski