Add IPNS Record code

[lidel]

This PR proposes adding ipns-record, like we already have one for libp2p-peer-record. ipfs/specs#369

Rationale / potential uses:

• Main one: we should add a dedicated codec for IPNS Record, otherwise people will use ipns(0xe5) code which would be invalid, as it indicates IPNS "namespace".
• IPIP-351 will ship in Kubo 0.19 and will allow fetching signed (verifiable) IPNS Record.
  • In the future /ipns/{id}?format=car could return a CAR with ipns-record as an additional block.
• IPNI wants to support IPNS Records, but need codec (Propose Naam as naming system powered by IPNI ipni/specs#4)

[rvagg]

Sorry for my ignorance on some of this, but is this intended to be used in CIDs, and is the block format the IPNS protobuf format?

[lidel]

@rvagg correct.

Block identified by CID with this codec can be parsed by following the protobuf from the IPNS spec: https://github.com/ipfs/specs/blob/main/ipns/IPNS.md#record-serialization-format