Add support for compressed keys

[jiyoontbd]

would like more input from @decentralgabe wrt this comment #262 (comment)

[decentralgabe]

DID DHT advocates for using compressed key representations when possible. Here's some more information on compression of elliptic curve keys also here.

Notably compression only matters with binary (or non-JWK) representations of keys, as JWKs do not support compressed key representations.

As a reference the ssi-sdk supports an open during conversion to/from public/private keys and their byte representations for compression and there's common library support for compressed key representations.