test(gfql/conformance): matrix cases for the #1673 scalar fns (floor/ceil/ceiling/round/toLower/toUpper)

The coverage ledger (cascaded from #1660) correctly flagged the new
GFQL_SCALAR_FUNCTIONS entries as neither exercised nor waived. Real 4-engine
parity-or-NIE cases beat waivers: each new function gets a cypher expression
case through the standard matrix driver (chain + DAG surfaces). dgx: matrix +
ledger 267 passed (cudf + polars-gpu lanes active).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: lmeyerov

graphistry/tests/compute/gfql/test_engine_polars_conformance_matrix.py

@@ -221,6 +221,15 @@ def _cypher_expression_queries():
         ("tostring_bool", "MATCH (n) RETURN n.id AS id, toString(n.flag) AS s"),
         ("tostring_int", "MATCH (n) RETURN n.id AS id, toString(n.num) AS s"),
         ("tostring_str", "MATCH (n) RETURN n.id AS id, toString(n.name) AS s"),
+        # #1673 numeric/string scalar fns (native on polars per the #1675 lowering; the
+        # coverage ledger requires every GFQL_SCALAR_FUNCTIONS entry exercised-or-waived)
+        ("floor", "MATCH (n) RETURN n.id AS id, floor(n.f) AS x"),
+        ("ceil", "MATCH (n) RETURN n.id AS id, ceil(n.f) AS x"),
+        ("ceiling", "MATCH (n) RETURN n.id AS id, ceiling(n.f) AS x"),
+        ("round", "MATCH (n) RETURN n.id AS id, round(n.f) AS x"),
+        ("round_p2", "MATCH (n) RETURN n.id AS id, round(n.f, 2) AS x"),
+        ("tolower", "MATCH (n) RETURN n.id AS id, toLower(n.name) AS s"),
+        ("toupper", "MATCH (n) RETURN n.id AS id, toUpper(n.name) AS s"),
         # NOTE: toString(float) is intentionally NOT here — polars declines it (NIE, covered by
         # test_tostring_float_honest_nie_polars), but cudf formats floats differently than pandas
         # (an orthogonal cudf float-repr divergence, like the list-literal element-order one), which