add iroh-hashseq codec

[cameronfyfe]

This adds a codec for hash sequence blobs used by Iroh.

Docs describing hash sequence blobs: https://iroh.computer/docs/layers/blobs#collections

[vmx]

To make sure I understand it correctly: This is a list of 32-byte long BLAKE3 hashes. One could say it's an IPLD Codec, as you could use it to build DAGs (you'd make CIDs with raw as Codec and blake3 as Multihash out of each hash).

What about giving it a more general name then, something like blake3-32-seq or so? Similar to what we've done at #343).

BTW: a maybe more permanent link to the spec is https://github.com/n0-computer/iroh.computer/blob/030f0b8104898327ca172ed5d1d84479d83208ad/src/app/docs/layers/blobs/page.mdx#collections

[cameronfyfe]

Thanks for the quick response.

Yes, my mental map of the codec was mapping to list<link> with pre-defined hash/codec as you described.

I can see the argument for making it more general. What about just blake3-hashseq? I could see any variation of {blake3|blake3-32|blake3-256}{hashseq|seq} making sense but that's my first choice.

[vmx]

blake3-hashseq sounds good to me. @rvagg what do you think?

[rvagg]

sgtm