On PHP 8.5, DateTimeImmutable::modify() warns when its result is
discarded, but CarbonImmutable overrides it and lost the attribute.
Override modify(), next(), previous() and __call() in CarbonImmutable
with #[NoDiscard] so a discarded result warns again. The attribute is
ignored on older PHP versions, and mutable Carbon is unchanged.
Existing immutable tests that discarded results now keep them; in
IsTest::testIsSameMonth this was a real slip, the loop never moved $dt.
Fixes#3377
A numeric $precision passed to round()/floor()/ceil() is always resolved
to the "second" unit. Once the precision reaches or exceeds 60 (e.g.
round(3600) meaning "nearest hour"), the rounding stayed confined to the
second field (range 0-59) and never carried into minute/hour/day, unlike
the equivalent string form (round('hour')).
Re-target the unit to minute/hour/day once the numeric precision reaches
that unit's own span in seconds, rescaling the precision accordingly,
mirroring the existing week -> day re-targeting already in roundUnit().
Sub-minute numeric precisions are unaffected.
dualfroz