operator * method
Multiply the price by another price, returning a new price. The other price must have the same base currency as this price's quote currency
Implementation
Price operator *(covariant Price other) {
assert(quoteCurrency == other.baseCurrency, 'TOKEN');
final fraction = super.multiply(other);
return Price.fromContractor(baseCurrency, other.quoteCurrency,
fraction.denominator, fraction.numerator);
}