Store best population during search

[LuKrO2011]

To avoid loosing everything when Pynguin crashes, we could keep track of the current best population during the search.

Combinations with the master-worker architecture might even allow continuing the search in case of a crash then.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 97.50000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 93.52%. Comparing base (b7b4fd4) to head (9291e84).
⚠️ Report is 158 commits behind head on main.

Files with missing lines	Patch %	Lines
src/pynguin/ga/searchobserver.py	97.14%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #131   +/-   ##
=======================================
  Coverage   93.52%   93.52%           
=======================================
  Files         282      282           
  Lines       35323    35363   +40     
  Branches     3015     3018    +3     
=======================================
+ Hits        33035    33075   +40     
- Misses       1701     1702    +1     
+ Partials      587      586    -1     

Files with missing lines	Coverage Δ
src/pynguin/configuration.py	100.00% <100.00%> (ø)
src/pynguin/ga/generationalgorithmfactory.py	87.89% <100.00%> (+0.10%)	⬆️
tests/ga/algorithms/test_randomalgorithm.py	100.00% <100.00%> (ø)
tests/utils/test_configuration_writer.py	98.79% <ø> (ø)
src/pynguin/ga/searchobserver.py	98.36% <97.14%> (-1.64%)	⬇️

... and 3 files with indirect coverage changes

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