Picosecond precision timestamp type, represented by an epoch time in seconds, a nanosecond offset, and
optional picosecond offset.
The nanosecond offset is from the start of the epoch second, so must be less than 1 billion.
The optional picosecond offset is only used for picosecond-precision data sources and is from the start of
the nanosecond, so must be less than 1000.