geotiff: pin open_geotiff(max_cloud_bytes=...) dispatcher silent drop (#1974)

[brendancol]

Summary

Test-coverage sweep pass 16 on the geotiff module. Closes a Cat 4 HIGH parameter-coverage gap on the open_geotiff dispatcher's max_cloud_bytes kwarg.

max_cloud_bytes was added in #1928 as an eager fsspec cloud-budget guard and re-ordered into the canonical reader signature by #1957. open_geotiff accepts the kwarg in its signature but only forwards it to _read_to_array on the eager non-VRT branch (xrspatial/geotiff/__init__.py:431). The GPU branch at line 410, the dask branch at line 422, and the VRT branch at line 362 never reference the kwarg, so:

open_geotiff(p, max_cloud_bytes=8, gpu=True)   # silently drops
open_geotiff(p, max_cloud_bytes=8, chunks=4)   # silently drops
open_geotiff(vrt, max_cloud_bytes=8)           # silently drops

Same class of dispatcher-silently-drops-backend-kwarg bug fixed by #1561, #1605, #1685, and #1810 for other backend-only kwargs. The two sibling kwargs on_gpu_failure (line 339) and missing_sources (line 355) already raise ValueError when used on a path where they do not apply.

Filed issue #1974 for the dispatcher fix. This sweep is test-only.

Tests

xrspatial/geotiff/tests/test_max_cloud_bytes_dispatcher_silent_drop_2026_05_15.py (11 tests, all behaving as designed locally):

• 4 xfail(strict=True) pinning the fix surface (gpu, dask, vrt, dask+gpu). Flip to xpass (= test failure under strict=True) when the dispatcher fix lands.
• 3 passing pins on the current silent-drop behaviour so the fix is visible as a diff.
• 4 positive pins that the eager local + file-like paths accept the kwarg (the docstring no-op contract).

Test plan

• All 11 tests pass / xfail as designed on the local host (pytest xrspatial/geotiff/tests/test_max_cloud_bytes_dispatcher_silent_drop_2026_05_15.py -v -> 7 passed, 4 xfailed).
• CI to confirm parity (the dask+gpu xfail skips when cupy / CUDA is unavailable).