Parse a timestamp or date string into canonical forms — zero-dependency. Accepts unix seconds/millis or any standard date string (ISO-8601, RFC-2822, etc.). Returns UTC ISO, unix seconds + millis, RFC-2822, calendar components (year/month/day/hour/minute/second/weekday), ISO weekday, ISO year+week, and day-of-year. Pass an IANA timezone (tz) to also get the DST-correct local wall-clock time and UTC offset. The reliable time primitive for agents normalizing or converting timestamps.