operator + method
Adds this power to another power.
The other
power is converted to the unit of this power before addition.
The result is a new Power instance with the sum, expressed in the unit
of this power (the left-hand operand).
Implementation
Power operator +(Power other) {
final otherValueInThisUnit = other.getValue(unit);
return Power(value + otherValueInThisUnit, unit);
}