feat: add jwk and jwk-set key codecs

Adds the JSON sister of the cose-key family from #400. Uses single-byte
codes adjacent to that block so JWK-based identifiers do not pay an
extra prefix byte forever.

* jwk (0x44): JSON-encoded JWK per RFC 7517 section 4
* jwk-set (0x45): JSON-encoded JWK Set per RFC 7517 section 5

The existing jwk_jcs-pub (0xeb51) and jwk_jcs-priv (0x1316) entries
remain; they are a strict canonical-JCS subset suited to stable peer
IDs. The new entries cover full RFC 7517 JWK as a self-describing
container; choose jwk_jcs-* when deterministic encoding matters and
jwk/jwk-set when interoperating with arbitrary RFC 7517 producers.

Author: lidel

table.csv

@@ -36,6 +36,8 @@ dns,                            multiaddr,      0x35,           permanent,
 dns4,                           multiaddr,      0x36,           permanent,
 dns6,                           multiaddr,      0x37,           permanent,
 dnsaddr,                        multiaddr,      0x38,           permanent,
+jwk,                            key,            0x44,           draft,      JSON-encoded JSON Web Key (JWK) per IETF RFC 7517 section 4; media type application/jwk+json; kty/alg/crv parameters identify the key algorithm; may carry public or private key material depending on which parameters are present
+jwk-set,                        key,            0x45,           draft,      JSON-encoded JWK Set per IETF RFC 7517 section 5; media type application/jwk-set+json; JSON object containing keys array of JWKs; each element processed independently
 protobuf,                       serialization,  0x50,           draft,      Protocol Buffers
 cbor,                           ipld,           0x51,           permanent,  CBOR
 raw,                            ipld,           0x55,           permanent,  raw binary