ISO 8601 calendar date without timezone.
Allows for every proleptic Gregorian date from Jan 1, 262145 BCE to Dec 31, 262143 CE.
Also supports the conversion from ISO 8601 ordinal and week date.
Extension trait for subsecond rounding or truncation to a maximum number
of digits. Rounding can be used to decrease the error variance when
serializing/persisting to lower precision. Truncation is the default
behavior in Chrono display formatting. Either can be used to guarantee
equality (e.g. for testing) when round-tripping through a lower precision
format.