Update GIS example models for Cell API changes

[EwoutH]

Problem

Three GIS example models in Mesa-examples are failing due to breaking changes introduced in mesa/mesa-geo#299, which added new keyword arguments (rowcol, xy) to the Cell.__init__() method.

Failing models:

• gis/urban_growth - UrbanCell
• gis/rainfall - LakeCell
• gis/population - UgandaCell

Error:

TypeError: <CustomCell>.__init__() got an unexpected keyword argument 'rowcol'

Root cause

The updated Cell.__init__() in mesa-geo now accepts keyword-only arguments rowcol and xy:

def __init__(self, model, pos=None, indices=None, *, rowcol=None, xy=None):

Custom Cell subclasses in the example models don't accept these arguments, causing instantiation to fail when RasterLayer._initialize_cells() tries to create cells.

Additional considerations

While fixing the signatures, we might update the models to use the new cell.rowcol property instead of the deprecated cell.indices where applicable.