Feature request: Implement `__repr__` methods for many classes

[Ram Rachum]

I was debugging some Gymnax code now. I had a box, and I tried to view what kind of box it is:

>>> box
<gymnax.environments.spaces.Box object at 0x000001D589442FC0>

It would be easier to introspect Gymnax experiments if a __repr__ method were implemented for Box and for many other classes.