Fixed-point decimal: the value is mantissa × 10^(−scale). This mirrors SQL
DECIMAL(38, scale) (Postgres/Spark cap precision at 38 digits, which is what
an i128 mantissa holds), and is lossless within that range — unlike Float.
Calendar/clock duration with month, day, second, and nanosecond components —
the model GQL/ISO 8601 uses (months and days are not fixed-length, so they are
kept distinct from seconds rather than collapsed). Construct from an ISO 8601
duration string such as P1Y2M10DT2H30M via Duration::parse.
Records a single-node upsert outcome into a report’s precise insert/update
counters. PutOutcome::Upserted and PutOutcome::Deduped carry no
insert-vs-update information and leave the counters unchanged.