Returns the list of units uniquely defining the value of this TemporalAmount.
The list of {@code TemporalUnits} is defined by the implementation class.
The list is a snapshot of the units at the time {@code getUnits}
is called and is not mutable.
The units are ordered from longest duration to the shortest duration
of the unit.
@implSpec
The list of units completely and uniquely represents the
state of the object without omissions, overlaps or duplication.
The units are _in order from longest duration to shortest.
@return the List of {@code TemporalUnits}; not null
Returns the list of units uniquely defining the value of this TemporalAmount. The list of {@code TemporalUnits} is defined by the implementation class. The list is a snapshot of the units at the time {@code getUnits} is called and is not mutable. The units are ordered from longest duration to the shortest duration of the unit.
@implSpec The list of units completely and uniquely represents the state of the object without omissions, overlaps or duplication. The units are _in order from longest duration to shortest.
@return the List of {@code TemporalUnits}; not null