refactor: use named tuples instead of dataclasses for timestep and state

[dluo96]

Is your feature request related to a problem? Please describe

Since the dataclasses we use are mutable, some side effects may occur when working with environment State and TimeStep.

Describe the solution you'd like

Use NamedTuple instead.

Describe alternatives you've considered

We could also freeze the dataclasses to be immutable but the NamedTuple option is preferred.

[aar65537]

This should be possible in python 3.11, but 3.9 and 3.10 don't allow a class to inherit from both NamedTuple and Generic (see python/cpython#88089). 3.8 does allow for generic named tuples, but I'm not sure if they really function correctly. I think the choices are to either drop support for 3.8, 3.9, and 3.10 or use frozen dataclasses.