fix(gfql): plan non-top-level optional match - #1487

Closes #1478.

Summary

• Route non-top-level OPTIONAL MATCH through LogicalPlan/PhysicalPlanner instead of the approved unplanned-chain fallback.
• Preserve specialized lowering logical plans when connected optional/scalar routes attach one.
• Remove non_top_level_optional_match from the residual fallback allowlist and update cutover coverage/changelog.
• Coordinate sibling TCK expectation promotion via Promote with5-2 direct cypher xfail tck-gfql#128 for with5-2.

Validation

• python3 -m pytest -q graphistry/tests/compute/gfql/test_runtime_physical_cutover.py -k 'not cudf' --tb=short
• python3 -m pytest -q graphistry/tests/compute/gfql/test_logical_planner.py --tb=short
• python3 -m pytest -q graphistry/tests/compute/gfql/cypher/test_lowering.py::test_compiled_query_sets_logical_plan_route_for_top_level_optional_shape graphistry/tests/compute/gfql/cypher/test_lowering.py::test_connected_optional_query_sets_query_graph_and_logical_plan graphistry/tests/compute/gfql/cypher/test_lowering.py::test_compiled_query_sets_logical_plan_route_for_optional_reentry_shape --tb=short
• ./bin/ruff.sh graphistry/compute/gfql/logical_planner.py graphistry/compute/gfql/cypher/lowering.py graphistry/compute/gfql_unified.py graphistry/tests/compute/gfql/test_logical_planner.py graphistry/tests/compute/gfql/test_runtime_physical_cutover.py
• ./bin/typecheck.sh graphistry/compute/gfql/logical_planner.py graphistry/compute/gfql/cypher/lowering.py graphistry/compute/gfql_unified.py
• git diff --check
• Rebase over origin/master@f3e0e2b504cd50aae2ca69289bdfba1831fe5762: resolved changelog conflict after GFQL deletion: native-plan shortestPath/path-alias multiple MATCH residuals #1489/Delete obsolete M1 differential scaffold tests #1491/DRY cuDF/pandas lowering test factory twins #1494; planner/tests auto-merged
• Review skill: reconverged after 4 total waves, including 2 clean post-rebase waves, no findings
• TCK sibling: Promote with5-2 direct cypher xfail tck-gfql#128 closed after rebasing empty; the same with5-2 expectation is already on tck-gfql/main via Align direct-Cypher contract for pygraphistry #1489 tck-gfql#133
• GitHub Actions: rerunning after final rebase/force-push
• Read the Docs external status: pass
• DGX RAPIDS 25.02 gfql on rebased head cfcb1e0: GFQL deletion: native-plan non-top-level OPTIONAL MATCH fallback bucket #1478 focused route tests passed, 2 passed
• DGX RAPIDS 26.02 gfql on rebased head cfcb1e0: GFQL deletion: native-plan non-top-level OPTIONAL MATCH fallback bucket #1478 focused route tests passed, 2 passed

Note

• Merge order: TCK dependency is already on tck-gfql/main via Align direct-Cypher contract for pygraphistry #1489 tck-gfql#133, so this PR can merge once current pygraphistry CI is green.
• Local full runtime cutover file and DGX 26.02 full focused file are constrained by CUDA availability/memory outside this PR: local host has no CUDA device; DGX had VLLM using ~81.9GiB and the newly merged GFQL deletion: native-plan scalar projection alias MATCH fallback bucket #1479 scalar cudf test OOMed before GFQL deletion: native-plan non-top-level OPTIONAL MATCH fallback bucket #1478. The GFQL deletion: native-plan non-top-level OPTIONAL MATCH fallback bucket #1478-specific 26.02 route passed under the same image.