@Nonnull
    static VariableAmount baseWithRandomAddition(double base, double addition) {
        return new BaseAndAddition(base, fixed(addition));
    }
Creates a new variable amount which has a base and an additional amount.
The final amount will be the base amount plus a random amount between
zero (inclusive) and the additional amount (exclusive).

@param base The base value
@param addition The additional amount
@return A variable amount representation
helper/src/main/java/me/lucko/helper/random/VariableAmount.java