Support units for `ByteCount` type

Overview

The Go SDK uses the ByteCount type to represent the number of bytes for instance memory, disks, and other Oxide resources. Instead of using values with units (e.g., 16GiB), users must convert these values to bytes (e.g., 17179869184). This can lead to issues if users leave off numbers or typo numbers. Some users opt to use a helper like the following to calculate the correct number of bytes.

> python3 -c 'print(16 * 1024**3)'
17179869184

This Go SDK should be updated to allow users to specify a value with a unit (e.g., 16GiB).

Implementation details

The implementation can take inspiration from the following.

• https://pkg.go.dev/k8s.io/apimachinery/pkg/api/resource#Quantity
• https://pkg.go.dev/github.com/dustin/go-humanize

Here are function signatures that an implementation can use.

func MustParseByteCount(str string) ByteCount
func ParseByteCount(str string) (ByteCount, error)

Given those function signatures, here's how a user can use them in code.

params := oxide.InstanceCreateParams{
  Memory: MustParseByteCount("16GiB"),
}

memory, err := ParseByteCount("16GiB")
if err != nil {
  // Handle error.
}

params := oxide.InstanceCreateParams{
  Memory: memory,
}

Anything else you would like to add?

No response

Start in types.go at the ByteCount definition, then review the linked Kubernetes Quantity and go-humanize references for unit-parsing behavior. Define how ParseByteCount and MustParseByteCount should handle values such as "16GiB", including invalid input, and verify that callers can use the resulting ByteCount in InstanceCreateParams.