[FEATURE] - Enforce descending y-coords

Is your feature request related to a problem? Please describe.
We quietly assume y-coords of structred grids are in descending order, but we often do not check this. Especially not for utility functions. Given that xarray has a tendency to flip coordinates into ascending order, y-coords often end up ascending. This can result into trouble such as in #825.

One way to deal with this is to create a decorator which forces descending y-coordinates for grid input and output of a function/method, similarly how we have a decorator to enforce the dim order of the output of a function/method.
An alternative would be input validation and presenting an error if y is not descending. This is already the case for the mf6 module, but I think expanding that to utility functions might be too strict and will frustrate user experience.

Start by reviewing the existing decorator that enforces output dimension order and the input validation already used by the mf6 module. Decide whether grid utilities should enforce descending y-coordinates through a decorator or reject ascending coordinates, then define tests covering grid inputs and outputs and the expected behavior.