"1 hour"            | "10 hours"          | hours(1)                            | "1h"
        "1 hour"            | "10 hours"          | hours(4.2123456)                    | "4h 12m 44s"
        "10 hours"          | "100 hours"         | hours(42.123456)                    | "42h 7m 24s"
        "100 hours"         | "None"              | hours(421.23456)                    | "421h 14m 4s"

type Format string

const (
	DecimalExponent = Format("DecimalExponent") // e.g., 12e6
	BinarySI        = Format("BinarySI")        // e.g., 12Mi (12 * 2^20)
	DecimalSI       = Format("DecimalSI")       // e.g., 12M  (12 * 10^6)
)

// MustParse turns the given string into a quantity or panics; for tests
// or other cases where you know the string is valid.
func MustParse(str string) Quantity {
	q, err := ParseQuantity(str)