EXTRACT(NANOSECOND) on Duration and Interval counts whole seconds twice #26678

Describe the bug

SELECT extract(nanosecond from arrow_cast(1500000000, 'Duration(Nanosecond)')),
       extract(nanosecond from interval '1.5 seconds'),
       extract(microsecond from interval '1.5 seconds');
-- 2500000000, 2500000000, 1500000

Expected behavior

1500000000 for both, consistent with microsecond.

Additional context

seconds_ns returns secs * 1_000_000_000 + subsecs. For Duration and Interval, date_part(Nanosecond) already includes the whole seconds. seconds_as_i32 takes subsecs % 1_000_000_000, and seconds_ns doesn't. This has been there since #20674 (54.0.0). Past i32::MAX nanoseconds the NULL-as-zero branch also drops the fraction, so interval '62.5 seconds' gives 2000000000, the Int32 overflow in #14738.

#26676 fixes EXTRACT(EPOCH) on Duration by computing from the i64 value, and #19807 fixed it on Interval from the interval fields. The same approach fits here.

Part of #26672.