Release-gate: eager-vs-dask raster equivalence for representative GeoTIFFs (PR 1 of 5 of epic #2341) #2357

Reason or Problem

Epic #2341 calls out that the highest release risk for the GeoTIFF surface is pixels matching while attrs, coords, or dims silently disagree across backends. Today, the eager (open_geotiff) and dask (read_geotiff_dask) entry points both promise stable behavior, but no single regression test asserts full raster equivalence — pixels + dims + coords + the seven release-attr keys — across the two paths on the same files.

Proposal

Add xrspatial/geotiff/tests/test_release_gate_eager_dask_parity_2341.py.

For each file in a representative-corpus list (integer dtype + nodata, float dtype + NaN nodata, MinIsWhite, masked_nodata-lifecycle), open it eagerly and via read_geotiff_dask, materialize the dask result, and assert all of:

• .values bit-exact (NaN-aware)
• .dims equal
• .coords element-wise equal under xr.testing.assert_identical-style strictness
• attrs['transform'], attrs['crs'], attrs['crs_wkt'], attrs['nodata'], attrs['masked_nodata'], attrs['georef_status'], attrs['raster_type'] all equal

The assertions are inlined as a small helper inside the test module (no new shared helper file — keeps the PR self-contained; consolidation across the PR-2..PR-5 sibling tests can be a follow-up). Add a row to docs/source/reference/release_gate_geotiff.rst citing the new test file under "Local GeoTIFF read and write".

Stakeholders and Impacts

Touches: one new test file under xrspatial/geotiff/tests/, one row added to the release-gate doc page. No production code changes. Runtime: bounded to the existing corpus fixtures already used by test_backend_pixel_parity_matrix_1813.py.

Out of scope (sibling PRs of epic #2341):

• Windowed-read shifted-transform parity (PR 2).
• Overview / sidecar metadata survival (PR 3).
• Stable-codec round-trip (PR 4).
• Negative tests for ambiguous metadata (PR 5).

Drawbacks

Slight overlap with test_backend_full_parity_2211.py, which already checks attrs finalization parity. This PR's test adds the eager-vs-dask cross-backend axis on top, and pins it under a release_gate-themed name so the release checklist row points at one test, not three.

Alternatives

• Extend test_backend_full_parity_2211.py instead of adding a new file. Rejected: the release-gate doc row needs a stable test path to cite; reusing an existing file couples the row to unrelated future edits.
• Make the assertions a shared helper module up front. Rejected: that requires sequential ordering across the five sibling PRs; inlining keeps PRs 1-5 independent.

Additional Notes or Context

Parent epic: #2341. Sibling issues to be created for PRs 2-5.