Ambiguity when exporting Ed25519 keys

There are two flavors of Ed25519 keys: legacy (PublicKeyAlgorithm::EdDSA + Curve::Ed25519) and new (PublicKeyAlgorithm::Ed25519).

After importing either of these flavors of keys, we cannot distinguish them when exporting (that is, the public key and the key's attributes are not enough).

Currently, we support exporting EdDSA, i.e., the legacy format. This also matches what sq key generate --cipher-suite Cv25519 (the default) does.

We should probably add something to the key ID to be able to distinguish these two types.