Plan path-alias carry matches natively - #1503

Summary

Fixes #1495. Blocks/unblocks #1486 residual fallback deletion work.

• Native-plans the final unused path-alias carry multiple_match_stages residual:
  MATCH path = shortestPath((a)-[*]-(b)) MATCH (b)-->(c) RETURN c
• Narrows the logical planner path-alias guard so carried scope baggage does not block the follow-on MATCH route.
• Adds fail-fast classification for unsupported shortestPath path-value references after a follow-on MATCH, such as length(path) / path IS NULL.
• Fixes a DGX-discovered cuDF/pandas interop failure in connected OPTIONAL MATCH start-node seeding by converting seed inputs to the concrete dataframe engine before isin().
• Updates the changelog.

Validation

• python3 -m pytest -q graphistry/tests/compute/gfql/test_logical_planner.py -k "path_alias or multiple_match" -> 3 passed, 23 deselected
• python3 -m pytest -q graphistry/tests/compute/gfql/test_runtime_physical_cutover.py -k "shortest_path or unplanned_chain or deferred_logical_plan" -> 9 passed, 20 deselected
• python3 -m pytest -q graphistry/tests/compute/gfql/test_logical_planner.py graphistry/tests/compute/gfql/test_runtime_physical_cutover.py -k "path_alias or multiple_match or shortest_path or unplanned_chain or deferred_logical_plan" -> 14 passed, 41 deselected
• python3 -m pytest -q graphistry/tests/compute/gfql graphistry/tests/compute/test_gfql.py -k "not cudf" -> 2231 passed, 29 skipped, 160 deselected, 15 xfailed
• python3 -m pytest -q graphistry/tests/compute/gfql/cypher/test_lowering.py -k "connected_optional_structured_matrix and not cudf" -> 3 passed, 1068 deselected
• ./bin/ruff.sh graphistry/compute/gfql/logical_planner.py graphistry/compute/gfql/cypher/lowering.py graphistry/compute/gfql/cypher/shortest_path_guards.py graphistry/compute/gfql_unified.py graphistry/tests/compute/gfql/test_logical_planner.py graphistry/tests/compute/gfql/test_runtime_physical_cutover.py -> pass
• ./bin/typecheck.sh -> pass
• python3 bin/ci_cypher_surface_guard.py -> pass
• git diff --check -> pass
• DGX RAPIDS 25.02 GFQL: 2398 passed, 22 skipped, 15 xfailed, 101 warnings in 95.52s; log /tmp/pygraphistry-1495-dgx/rapids-25.02-gfql.log
• DGX RAPIDS 26.02 GFQL: 2398 passed, 22 skipped, 15 xfailed, 100 warnings in 81.58s; log /tmp/pygraphistry-1495-dgx/rapids-26.02-gfql.log
• git fetch origin master; git merge-base --is-ancestor origin/master HEAD -> current origin/master still included, no rebase needed

Review

• Review skill artifacts: plans/path-alias-carry-1495/review/
• Credentials scan clean.
• Wave 1: no findings.
• Wave 2: no findings.
• Wave 3: no findings after post-amend helper/cuDF/surface-baseline changes.
• Wave 4: no findings.
• Review converged.

Pending

• None. PR is validated and intentionally left unmerged.