Adding Model checkpoint

[The-Blitz]

I saw #137 was still open so i wanted to try it out and help creating checkpoints.

Basically I used the LogbookSaver as it was suggested and then used pickle to enable the save and load functions (maybe that was not the expected way)

I hope this helps

[rodrigo-arenas]

Hi @The-Blitz thanks for this work, it looks like the general approach is aligned with the package features, I'll be checking it with more detail and making some tests

[codecov]

Codecov Report

Attention: Patch coverage is 57.14286% with 36 lines in your changes missing coverage. Please review.

Project coverage is 95.39%. Comparing base (f9a643a) to head (39baa19).
Report is 7 commits behind head on master.

Files with missing lines	Patch %	Lines
sklearn_genetic/genetic_search.py	44.64%	31 Missing ⚠️
sklearn_genetic/callbacks/model_checkpoint.py	81.48%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #158      +/-   ##
==========================================
- Coverage   98.40%   95.39%   -3.02%     
==========================================
  Files          25       26       +1     
  Lines        1067     1151      +84     
==========================================
+ Hits         1050     1098      +48     
- Misses         17       53      +36     

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