Implements fee calculation. The fee structure of Fuel may change over time, but not between
roll-outs of new Fuel DNAs. Therefore, its values and limits can be hard-coded here.
The Fuel Fuel type and math functions, and JSON serialization support. Supports Fraction
type for computing fractional Fuel amounts using rational numbers; useful for expressing
“percentages” of Fuel amounts without losing (too much) precision, while retaining the
ability to compute Fuel transaction fees on the largest possible transaction amounts.