#989 follow-through: retire post-#1260 lowering reentry shims

[lmeyerov]

Summary

• retire transitional lowering-level bounded-reentry delegator shims introduced during the Meta: GFQL monolith shrinkdown (lowering.py + CompiledCypher cleanup) #1260 split
• keep bounded reentry helper ownership in graphistry/compute/gfql/cypher/reentry/runtime.py and call runtime helpers directly from lowering use sites
• trim split-guard tests by removing assertions that depended on retired lowering reentry wrappers
• add Development changelog note for the Cypher/GFQL: introduce a first-class row-carrier IR for multi-stage vectorized row semantics #989 follow-through cleanup

Validation

• uv run ruff check graphistry/compute/gfql/cypher/lowering.py graphistry/tests/compute/gfql/cypher/test_lowering_s3_split_guard.py
• python -m pytest -q graphistry/tests/compute/gfql/cypher/test_lowering_s3_split_guard.py graphistry/tests/compute/gfql/cypher/test_lowering.py -k "compile_cypher_records_reentry_plan_for_multi_whole_row_prefix or compile_cypher_records_freeform_reentry_plan_contract or executes_simple_freeform_intermediate_reentry_match"

Refs #989

[lmeyerov]

Temporary close/reopen to refresh stale refs/pull/1327/head used by ReadTheDocs checkout.

[lmeyerov]

Superseded by #1334 due ReadTheDocs hidden pull-ref desync on this PR number.