operator + method
Adds another BigDecimal to this one.
Implementation
BigDecimal operator +(BigDecimal other) {
int maxScale = _scale > other._scale ? _scale : other._scale;
BigDecimal a = setScale(maxScale);
BigDecimal b = other.setScale(maxScale);
BigInt result = a._unscaledValue + b._unscaledValue;
return BigDecimal._(result, maxScale);
}