Module temporal

Duration and Instant types — pure-Silo temporal values.

Covers IDuration with constructors, accessors, simple arithmetic, and Eq / Ord, plus Instant as a record with a pure-Silo .duration-since.

Unsigned-duration arithmetic, IDuration + IDuration, subtraction combinations, .mul-f64 / .div-f64 / .checked-* / .saturating-*, .elapsed, and a Display impl land once the supporting operator specialisation, +Panic, +Temporal effect, and FmtSpec-aware .fmt arrive.