fix(integ): use engine-zone today in DateTimeFunctionIT now()-based assertions

[ahkcs]

Summary

DateTimeFunctionIT's adddate/subdate-with-TIME tests assert against a current date the query engine supplies — e.g. adddate(TIME('07:40:00'), interval 1 day) → today+1. The expected value was computed with LocalDate.now() (JVM default zone), but the analytics-engine route resolves now()/curdate() in UTC. When a run starts after the local/UTC date boundary (e.g. 17:xx PDT = 00:xx UTC), the two dates differ by one day and the now()-based tests fail with an off-by-one-day timestamp.

Same class of bug fixed for DateTimeComparisonIT in #5543, surfacing in a different IT — newly visible because the analytics route only recently gained now()-family support.

Fix

Add an engineToday() helper:

private LocalDate engineToday() {
  return isAnalyticsParquetIndicesEnabled() ? LocalDate.now(ZoneOffset.UTC) : LocalDate.now();
}

and route the 10 LocalDate.now() assertion sites through it. The v2/Calcite-over-Lucene branch (: LocalDate.now()) is byte-identical to the prior behavior, so that path cannot regress; only the analytics route changes to match the engine's UTC clock. Pure test change, no production code.

Before / After

CalciteDateTimeFunctionIT on the analytics-engine route, run started 17:32 PDT = 00:32 UTC (inside the boundary window):

Test	Before	After
testDateAdd	FAIL (off by 1 day)	PASS
testDateSub	FAIL	PASS
testAddDateWithDays	FAIL	PASS
testSubDateDays	FAIL	PASS
testAddDateWithInterval	FAIL	PASS
testSubDateInterval	FAIL	PASS
class total	57/65	60/65

The 2 still-failing tests (testDateFormat %c zero-padding, testStrftimeWithDateFields sub-millisecond precision) are unrelated backend format/precision gaps, out of scope here.

Test plan

• ./gradlew :integ-test:integTestRemote --tests '*.CalciteDateTimeFunctionIT' against an analytics-engine cluster, run inside the UTC-boundary window — the 6 now()-based tests pass.
• v2 branch is byte-identical to the original LocalDate.now() — no behavior change off the analytics route.