Fix Cypher node identity column handling - #1504

Closes #1490

Summary

• Replaces hardcoded internal node-identity id references in Cypher lowering with an internal __gfql_node_id__ token.
• Resolves that token to the graph's bound node column at same-path and row-pipeline execution time.
• Keeps a user data property named id projectable and distinct from internal node identity.
• Adds pandas and cuDF regressions for repeated node aliases, distinct/grouped node identity, and id property projection.

Notes

• External TCK coordination is in Update direct Cypher match7-24 xfail contract tck-gfql#135; this checkout does not edit tck-gfql.
• Existing unsupported repeated-alias property projection remains out of scope; repeated-alias identity filtering and aggregate counting are covered.

Validation

• python3 -m pytest -q graphistry/tests/compute/gfql/cypher/test_lowering.py::test_lower_match_query_rewrites_duplicate_node_aliases_to_internal_identity_checks graphistry/tests/compute/gfql/cypher/test_lowering.py::test_string_cypher_duplicate_node_alias_identity_shape_uses_bound_node_column graphistry/tests/compute/gfql/cypher/test_lowering.py::test_issue_1490_repeated_node_alias_uses_bound_node_identity graphistry/tests/compute/gfql/cypher/test_lowering.py::test_issue_1490_user_id_property_remains_projectable_with_custom_identity graphistry/tests/compute/gfql/cypher/test_lowering.py::test_issue_1490_distinct_and_grouping_use_bound_identity_not_user_id -> 5 passed
• python3 -m pytest -q graphistry/tests/compute/gfql/cypher/test_lowering.py -k 'issue_1490 or duplicate_node_alias or custom_node_column_name or count_distinct or grouping_use_bound_identity or whole_row_grouping' -> 13 passed
• python3 -m pytest -q graphistry/tests/compute/gfql/cypher/test_lowering.py -k 'not cudf' -> 949 passed, 12 skipped, 113 deselected
• ./bin/ruff.sh -> passed
• ./bin/typecheck.sh -> passed
• git diff --check -> passed
• python3 bin/ci_cypher_surface_guard.py -> passed (lowering.py at 9038/9038 baseline)
• DGX RAPIDS 25.02 (PROFILE=gfql, GPU): Cypher engine hardcodes id as the node-identity column #1490 cuDF regression + two GFQL cuDF smokes -> 3 passed
• DGX RAPIDS 26.02 (PROFILE=gfql, GPU): Cypher engine hardcodes id as the node-identity column #1490 cuDF regression + two GFQL cuDF smokes -> 3 passed
• TCK coordination PR Update direct Cypher match7-24 xfail contract tck-gfql#135 local validation against this branch:
  • PYTHONPATH=/home/lmeyerov/Work/pygraphistry2 python3 -m pytest -q tests/cypher_tck/test_tck_runner.py::test_direct_cypher_xfail_contract --maxfail=1 -> 724 passed
  • PYTHONPATH=/home/lmeyerov/Work/pygraphistry2 python3 -m pytest -q tests/cypher_tck/test_direct_cypher_contract_fastfail.py::test_direct_cypher_nonvalidation_outcome_snapshot_fastfail -> 1 passed
  • PYTHONPATH=/home/lmeyerov/Work/pygraphistry2 python3 -m pytest -q tests/cypher_tck/test_report.py::test_direct_cypher_nonvalidation_samples_are_stable_and_bounded tests/cypher_tck/test_report.py::test_build_report_includes_gap_priority_sections -> 2 passed
• GitHub CI: green after rerunning paired tck-gfql jobs (76419264072, 76419266901)