Implement __slots__ to avoid user confusion

[MicahGale]

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]

Some thoughts. First, this is going to be labor intensive. What if instead we just overrode __setattr__ for instances and not the class that essentially always raised an AttributeError? This may cause issues with properties in which more complicated logic could work.

Another option is this library: https://github.com/cjrh/autoslot