Timeframe gained new/millis/seconds/one_minute_ms; add minutes, hours and
days alongside them. Each builds on seconds (minutes(5) -> a 300-second
bucket), consistent with Timeframe::seconds, and guards the multiplication
with checked_mul so an oversized n yields Error::InvalidTimeframe instead
of an overflow panic. A non-positive n is rejected by Timeframe::new.
Each method carries a runnable doctest, and unit tests cover the known
bucket sizes, non-positive rejection and overflow rejection.
kingchenc
d5ff0a9df6