feat(stream): add MaybeConsumable.getValue helper method

export type MaybeConsumable<T> = T | Consumable<T>;

export namespace MaybeConsumable {

    export function getValue<T>(value: MaybeConsumable<T>): T {

        return value instanceof Consumable ? value.value : value;

    }

    export function tryConsume<T, R>(

        value: T,

        callback: (value: T extends Consumable<infer U> ? U : T) => R,