geotiff tests: consolidate kwarg / signature cluster (Sub-PR A)

[brendancol]

Closes #2431 (Sub-PR A of two). Cluster 7 of the long-tail GeoTIFF test consolidation epic (#2424). Tests-only.

Summary

Fold nine top-level kwarg and signature files into a new xrspatial/geotiff/tests/unit/test_signatures.py, grouped into six sections by concern:

• test_signature_annotations_1654.py
• test_signature_annotations_1705.py
• test_reader_kwarg_order_1935.py
• test_experimental_internal_optin_2352.py
• test_photometric_kwarg_1769.py
• test_gil_friendly_kwarg_1830.py
• test_kwarg_coverage_2026_05_11_r4.py
• test_kwarg_behaviour_2026_05_12.py
• test_kwarg_behaviour_2026_05_12_v2.py

The six sections are parameter annotations (#1654, #1705), canonical reader kwarg order (#1935), experimental / internal-only opt-in gates (#2352), the photometric kwarg and extra_tags override (#1769), the gil_friendly deflate kwarg (#1830), and reader / writer kwarg behaviour from the 2026-05-12 coverage sweep.

GPU gating moves to the shared requires_gpu marker from _helpers/markers.py, replacing the per-file _gpu_available helpers. No assertion changed.

Audit

xrspatial/geotiff/tests/CLUSTER_AUDIT_KWARG.md maps every old file::test to its new file::test_id. The audit file is deleted in a final pre-merge commit.

Verification

• pytest xrspatial/geotiff/tests/unit/test_signatures.py -v: 167 passed (same total as the nine source files).
• pytest xrspatial/geotiff/tests/ --co -q: 5891 tests collected, no errors.

Test plan

• New unit/test_signatures.py passes on this checkout (GPU present).
• Full xrspatial/geotiff/tests/ suite collects.
• CI green across numpy / cupy / dask+numpy / dask+cupy.
• Audit file deleted on the pre-merge commit.

[brendancol]

PR Review: geotiff tests consolidate kwarg / signature cluster (Sub-PR A)

Tests-only consolidation. I read the new unit/test_signatures.py in full and compared it against the nine deleted source files. The domain-specific checks (algorithm accuracy, backend dispatch, dask/cupy kernels) do not apply here since no source changed, so the review is about whether the consolidation keeps coverage intact and stays correct.

Blockers

None.

Suggestions

None.

Nits

• xrspatial/geotiff/_encode.py:382 and :529 have comments that name test_gil_friendly_kwarg_1830, which this PR deletes. The pinned contract now lives in unit/test_signatures.py::test_write_tiled_parallel_passes_gil_friendly_positionally, so those comments are now stale. This is out of scope for a tests-only PR (no source edits), so I am flagging it for a follow-up rather than fixing it here.

What looks good

• Test count is preserved exactly: 167 collected before and after.
• No test was dropped or merged. The audit file maps every old file::test to its new id.
• GPU gating moved from the per-file _gpu_available / _gpu_only helpers to the shared requires_gpu marker (20 decorations), which satisfies the issue's "markers from _helpers/markers.py" constraint.
• Shared helpers lifted to module scope (_annotated_smoke_da, and _write_tile_to_vrt using the module-level write import) with no duplicate top-level defs, classes, or fixtures.
• No leftover imports of the deleted files anywhere in the tree.
• isort and flake8 clean.

Checklist

• Test count preserved (167 -> 167)
• GPU tests still gated correctly (requires_gpu)
• No dropped or duplicated tests
• Audit file maps every old test to its new id
• Imports resolve; lint clean
• [n/a] Algorithm / dask / cupy correctness (no source changed)
• [n/a] README feature matrix (tests-only)