Fix examples for Mesa 2.2.0 API change

[rht]

Update examples to always initialize all Mesa models with super().__init__().

class MyModel(mesa.Model):
    def __init__(self):
        super().__init__()  # This is now required!

This is needed to correctly add Agents to the model and setup other Mesa model variables.

[rht]

Ready for review. This PR fixes all the issues except for the weakref stuff, which needs to happen in projectmesa/mesa itself.

[tpike3]

Thanks for doing this @rht!