#63343)

### What problem does this PR solve?
SimplifyInPredicate could incorrectly remove narrowing DATETIMEV2 casts
inside IN predicates.
For expressions such as `CAST(datetimev2(6) AS DATETIMEV2(3)) IN (...)`,
the rewrite could turn the predicate
into a direct comparison on the original DATETIMEV2(6) column, which is
not semantics-preserving because the cast
uses precision reduction and rounding. The rule also used a binary-based
microsecond alignment check instead of a
decimal scale check, which could incorrectly treat some literals as
losslessly convertible.

This change restricts the rewrite to non-narrowing DATETIMEV2 casts and
fixes the literal alignment check to use
decimal scale factors. It also adds FE unit tests and a regression case
for the reported DATETIMEV2 scenario.