Implement __slots__ to avoid user confusion

[MicahGale]

Discussed in #345

^{Originally posted by MicahGale August 2, 2023}
TIL about slots in python: https://stackoverflow.com/questions/472000/usage-of-slots

Basically statically allocating python attributes. The benefit would be to guard against typos frustrating users. For instance cell.materail = mat.

[MicahGale]

The official strategy for this now is:

1. All top level abstract classes have overwritten __setattr__ to avoid typos.
2. __slots__ is only used for simple immutable classes where it is easy to enumerate everything.

For now this is all that will be done, and fully implementing slots is not the true solution for what is desired, and would be too costly to do effectively.