SubtreeMutation bugfix, run-examples CI/CD, requirements update

[itaitzruia4]

• Fixed a bug where SubtreeMutation would create a dummy individual with no assigned value for higher_is_better, causing the program to crash.
• Added matplotlib to requirements file, since one of the examples depend on it.
• Added a workflow that automatically runs all examples and fails if an error is raised.
• Improved formatting of some of the examples, and modified the individual tree execution in MuxEvaluator
  from:

individual.execute(s0=s0, s1=s1, s2=s2, d0=d0, d1=d1, d2=d2, d3=d3, d4=d4, d5=d5, d6=d6, d7=d7)

to

individual.execute(**select_entries, **input_entries)

[itaitzruia4]

I'll reopen this after finishing with the examples tests workflow

[achiyae]

the tests of 3.9 failed for some reason. maybe it's flakiness?

[itaitzruia4]

Closing untill I add the hyperparameter change feature