Delete obsolete M1 differential scaffold tests - #1491

Closes #1472.

Summary

• Deleted the obsolete M1 legacy-vs-candidate differential scaffold test file.
• Preserved the unique independent OPTIONAL MATCH row/null behavior as a direct lowering test, including both optional-clause orders.
• Updated CHANGELOG.md.

Audit

• ic1-independent-optional-arms and reversed order: promoted to direct test_issue_1472_independent_optional_arms_preserve_per_row_nulls.
• with-boundary-binding-row-regression: already covered by direct runtime test_issue_1047_multi_row_scalar_prefix_both_tags_matched and binder lineage test_binder_with_boundary_scope_lineage.
• Binder prepass invocation: already covered by test_compile_cypher_invokes_binder_prepass, test_compile_cypher_rebinds_after_normalization, and test_cypher_to_gfql_invokes_binder_prepass.
• Optional null-extension trust: already covered by test_binder_optional_match_tracks_null_extended_from and direct optional-only alias detection tests.

LOC delta

• CHANGELOG.md: +1 / -0
• graphistry/tests/compute/gfql/cypher/test_lowering.py: +41 / -0
• graphistry/tests/compute/gfql/cypher/test_m1_differential_scaffold.py: +0 / -282
• Net: +42 / -282, overall -240 LOC

Validation

• python3 -m pytest -q graphistry/tests/compute/gfql/cypher/test_lowering.py::test_issue_1472_independent_optional_arms_preserve_per_row_nulls graphistry/tests/compute/gfql/cypher/test_binder.py::test_binder_optional_match_tracks_null_extended_from graphistry/tests/compute/gfql/cypher/test_binder.py::test_binder_with_boundary_scope_lineage graphistry/tests/compute/gfql/cypher/test_lowering.py::test_issue_1047_multi_row_scalar_prefix_both_tags_matched
  • 5 passed, 4 warnings
• python3 -m pytest -q graphistry/tests/compute/gfql/cypher/test_binder.py graphistry/tests/compute/gfql/cypher/test_lowering.py -k 'not cudf'
  • 1022 passed, 12 skipped, 113 deselected, 65 warnings
• ./bin/ruff.sh
  • passed
• ./bin/typecheck.sh
  • passed
• git diff --check
  • passed

GPU/RAPIDS note

This PR is a test-only deletion/preservation slice and does not change cuDF/GPU runtime code. The full local binder/lowering command without -k 'not cudf' hit local environment failures because cudf is installed but no CUDA device is present (cudaErrorNoDevice); the non-cuDF slice and focused replacement tests pass locally.

CI note

The pygraphistry tck-gfql workflow resolves a same-named graphistry/tck-gfql branch before falling back to main. A matching issue-1472-delete-m1-diff-scaffold TCK branch was created at the open with5-2 rebaseline PR head (graphistry/tck-gfql#128) so this PR uses the current direct-Cypher expectation while that TCK baseline is awaiting merge.