fix(cypher): support reentry MATCH WHERE WITH - #1028

Summary

• support alternating reentry shapes of the form MATCH ... WITH ... MATCH ... WHERE ... WITH ... MATCH ... RETURN
• attach the post-reentry WHERE to the correct current reentry stage during bounded reentry compilation
• move the exact #1000 IC6 query past the earlier post-reentry-WHERE parser barrier to the next UNWIND after post-WITH MATCH blocker
• lock the new parser boundary so direct MATCH after post-WITH WHERE and multi-WHERE reentry shapes still fail fast explicitly

Scope

This is Phase 2 of #1000, stacked on top of Phase 1 PR #1027.

What it covers:

• connected MATCH ... WITH ... MATCH ... WHERE ... WITH ... MATCH ... RETURN
• carried-scalar variants of that same reentry shape
• empty-result behavior for the new WHERE ... WITH reentry path
• exact IC6 blocker progression from post-reentry WHERE to post-reentry UNWIND

What it does not cover yet:

• UNWIND between reentry stages
• the remaining IC6 comma-pattern reentry fanout around post

Links

• Refs Cypher lowering does not support WITH ... UNWIND after MATCH-introduced graph aliases #1000
• Stacked on fix(cypher): support expression-valued pattern properties #1027
• Umbrella issue: Cypher lowering does not support WITH ... UNWIND after MATCH-introduced graph aliases #1000
• Umbrella draft PR: fix(cypher): tackle #1000 IC6 residual UNWIND/MATCH gap #1022
• Phase 1 PR: fix(cypher): support expression-valued pattern properties #1027

Amplification notes

The follow-on coverage on this branch also locks the intended fail-fast boundaries around the parser state change:

• direct MATCH after post-WITH WHERE is still rejected
• multiple post-reentry WHERE clauses are still rejected explicitly

Testing

• python3.12 -B -m pytest -q graphistry/tests/compute/gfql/cypher/test_lowering.py -k 'multi_stage_with_match_reentry_connected_shape or multi_stage_with_match_reentry_carried_scalar_shape or multi_stage_with_match_reentry_with_intermediate_where or failfast_rejects_direct_match_after_post_with_where_without_intervening_with or failfast_rejects_multiple_post_with_where_clauses or issue_1000_ic6_after_phase2_now_stops_at_post_with_match_unwind'
• python3.12 -B -m pytest -q graphistry/tests/compute/gfql/cypher/test_lowering.py -k 'same_path_expression_valued_pattern_property or non_property_dynamic_pattern_expression_runtime or reentry_identifier_valued_pattern_property or reentry_relationship_expression_valued_pattern_property'
• ruff check graphistry/compute/gfql/cypher/parser.py graphistry/compute/gfql/cypher/lowering.py graphistry/tests/compute/gfql/cypher/test_lowering.py