Consider a unique definition for Wavefunction

[rmlarose]

Wavefunction is currently multiply defined, once as the class and once as a getter function for the class. This caused a few issues with mypy, and while they are easily resolved by importing the correct Wavefunction, there is a chance for confusion. Perhaps refactor the function to get_wavefunction or a similar name?

[wjhuggins]

This causes additional problems with Pylance in VSCode. It really would be a nice change even if it's annoying to break people's code.

[wjhuggins]

Would a PR that does this be approved?