PVDeg uses deprecated xarray.Dataset.drop() syntax

[tobin-ford]

Describe the bug
PVDeg uses xarray.Dataset.drop() syntax in geospatial.py:383 and utilties.py:1567

To Reproduce
Call pvdeg.utilities.gids_dataset_to_coords_dataset or pvdeg.geospatial.zero_template

/kfs3/scratch/tford/envs/render/lib/python3.13/site-packages/pvdeg/utilities.py:1567: FutureWarning: dropping variables using drop is deprecated; use drop_vars.
stacked = ds_gids.drop(["gid"])

Desktop (please complete the following information):

• pvdeg: 0.7.1
• xarray: 2026.2.0
• Python: 3.13.0