Instead of saving bytes, save a string, which makes String() faster
and does not unduly penalize marshal. During parse, save the string
if it is in canonical form.
Provides fast transformations of int64 scaled values with overflow to
inf.Dec as needed. Attempts to reduce allocations and expensive
operations in the critical path.
Alters the public signature of Quantity to encourage more efficient use
Treat `nil` Amount as 0 in `resource.Quantity.Add` and
`resource.Quantity.Sub`. Also, allow adding/subtracting resources with
different Formats (since Format has no effect on the underlying value).
