Summary

The eager numpy, dask, and tiled-GPU read paths all gate the windowed
coord computation on geo_info.has_georef so a TIFF with no GeoTIFF
tags returns int64 file-relative pixel coords.

read_geotiff_gpu's stripped-fallback branch only checked t is None,
which is never true for non-georef files (_extract_transform returns
a default unit GeoTransform with has_georef=False). The branch
synthesised float64 coords like [-0.5, -1.5, ...] from that
placeholder, breaking backend parity on every stripped, non-georef
windowed GPU read.

The tiled-GPU helper _gpu_apply_window_band already handles this
correctly; this PR brings the stripped branch in line.

Reproducer

import numpy as np
from xrspatial.geotiff import open_geotiff
from xrspatial.geotiff._writer import write

arr = np.arange(64, dtype=np.float32).reshape(8, 8)
write(arr, "/tmp/no_georef.tif", compression='none', tiled=False)

eager = open_geotiff("/tmp/no_georef.tif", window=(0, 0, 4, 4))
gpu = open_geotiff("/tmp/no_georef.tif", gpu=True, window=(0, 0, 4, 4))

eager.y.dtype, eager.y.values   # int64 [0 1 2 3]
gpu.y.dtype, gpu.y.values       # float64 [-0.5 -1.5 -2.5 -3.5]  -- before fix

Fix

read_geotiff_gpu line ~2727: route not has_georef (and the
pre-existing t is None failure mode) through the integer pixel-coord
branch, using offset-based np.arange(r0, r1) so file-relative
semantics match the eager and dask paths.

Test plan

• New regression tests in test_no_georef_windowed_coords_1710.py
  cover the GPU offset-window case and the no-transform-attr case
• All 17 tests in test_no_georef_windowed_coords_1710.py pass
• All 86 metadata-propagation tests pass (test_attrs_parity_1548,
  test_metadata_round_trip_1484, test_dask_int_nodata_chunks_1597,
  test_coords_to_transform_3d_1643, test_gpu_nodata_1542,
  test_gpu_writer_attrs_1563, test_overview_nodata_inheritance_1739)
• 4-backend parity verified end-to-end (numpy, cupy,
  dask+numpy, dask+cupy) on the stripped-non-georef-windowed case

Resolves #1753.