Grid Ops and SW refactor

[jejjohnson]

Updated the Linear and NonLinear SW example using the functional API. (Later we can add a higher-level API).

Interp API

u: Array["Nx Ny"]  = ...
u: Array["Nx-1 Ny"]  = grid.interp(u: Array = u, axis: int=0, method: str="linear")

Difference API

This will take the finite difference method given an axis

# init field and domain
u: Array["Nx Ny"] = ...
domain: Domain = ...
# take the difference
u: Array["Nx-1 Ny"]  = grid.difference(u: Array = u, step_size: int=domain.dx[0], axis: int=0, method: str="right")