Support truncated hashes

[achingbrain]

It's common practice to truncate some message digests (see 5.1 of Recommendation for Applications
Using Approved Hash Algorithms).

This proposal is to add a truncate option to hasher.digest and also enforcing min/max hash lengths:

const sha512 = from({
  name: 'sha2-512',
  code: 0x13,
  encode: input => coerce(crypto.createHash('sha512').update(input).digest()),

  // constrain digest truncation - default options are shown, inspired by
  // https://github.com/ipfs/boxo/blob/main/verifcid/cid.go#L17-L20
  // minDigestLength: 20,
  // maxDigestLength: 128

  // use default minDigestLength but constrain max to value specific to hash algorithm
  maxDigestLength: 64
})

// input data
const buf = Uint8Array.from([0, 1, 2, 3])

// sha2-512 hash truncated to 32 bytes
const digest = await sha512.digest(buf, {

  // passing < minDigestLength or > maxDigestLength would cause this to throw
  truncate: 32
})