Reading uint TIFF with negative GDAL_NODATA sentinel raises OverflowError #1581

Summary

A uint TIFF whose GDAL_NODATA tag is set to a negative sentinel (e.g. -9999) raises OverflowError on read instead of masking the nodata pixels to NaN. The -9999 sentinel is common on unsigned-integer rasters because many GDAL pipelines write the tag as a string without checking dtype range. Both rasterio and GDAL promote the array to float and mask in this case; xarray-spatial fails the cast.

Reproduction

import numpy as np
import xarray as xr
from xrspatial.geotiff import to_geotiff, open_geotiff

arr = np.array([[1, 2, 3], [4, 5, 6]], dtype=np.uint16)
da = xr.DataArray(arr, dims=['y', 'x'])
to_geotiff(da, '/tmp/test.tif', crs=4326, nodata=-9999)

open_geotiff('/tmp/test.tif')
# OverflowError: Python integer -9999 out of bounds for uint16

Affected backends

The same cast pattern lives in four places, so every backend hits the OverflowError:

• xrspatial/geotiff/__init__.py ~line 557: numpy eager read (open_geotiff)
• xrspatial/geotiff/__init__.py ~line 625: _apply_nodata_mask_gpu (cupy read)
• xrspatial/geotiff/__init__.py ~line 1528: _delayed_read_window (dask read)
• xrspatial/geotiff/_reader.py: _resolve_masked_fill and _sparse_fill_value (LERC masked fill + sparse tile fill)

Each does arr.dtype.type(int(nodata)) or dtype.type(int(v)) with no range check.

Expected behavior

For any integer dtype with an out-of-range nodata sentinel, promote to float64 and skip the sentinel comparison (no value in the file can match anyway). Keep attrs['nodata'] set to the user-declared value so write round-trips preserve it. This matches rasterio's behavior.

Severity

HIGH (Cat 2 NaN propagation). This crashes the read of a class of TIFFs that are widespread in practice. Behavior matches across numpy / cupy / dask, so it is a shared accuracy bug rather than a backend divergence.