If we are going to nanosecond precision, I'm a little surprised Temporal doesn't include a `TAIInstant`? Maintaining a leap-second table (and the conversion log

If we are going to nanosecond precision, I'm a little surprised Temporal doesn't include a `TAIInstant`? Maintaining a leap-second table (and the conversion logic) sucks for the same reason that maintaining your own copy of tzdata sucks. It really wouldn't need any methods other than a (possibly lossy) conversion to or from the corresponding UTC `Instant`.