test(gfql): lower pandas-lane execution.py coverage floor 84.75->83.5

WITH...MATCH reentry added polars-specific branches to the shared reentry/execution.py.
Those are covered by the polars test lane (changed-line 100%) but unreachable by the
pandas core lane, which legitimately drops its per-file coverage to 83.81%. Lower the
pandas-lane floor to match; the polars branches keep real coverage via test-polars.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Y6dQEcjdazEnzuvuwf73ZL

Author: lmeyerov

graphistry/tests/compute/gfql/coverage_baselines/ci-pandas-py3.12.json

@@ -35,7 +35,7 @@
     "graphistry/compute/gfql/cypher/reentry/__init__.py": 100.0,
     "graphistry/compute/gfql/cypher/reentry/carry.py": 82.05,
     "graphistry/compute/gfql/cypher/reentry/compiletime.py": 85.48,
-    "graphistry/compute/gfql/cypher/reentry/execution.py": 84.75,
+    "graphistry/compute/gfql/cypher/reentry/execution.py": 83.5,
     "graphistry/compute/gfql/cypher/reentry/flatten.py": 94.05,
     "graphistry/compute/gfql/cypher/reentry/lowering_support.py": 88.38,
     "graphistry/compute/gfql/cypher/reentry/naming.py": 100.0,