This enhancement proposes adding a `getPublicKey` method to the `PrivateKey` interface. Several new algorithms require obtaining the public key associated with a private key, either by computing it from the private key material or by retrieving it when the public key is stored together with the private key. For example, RFC 9180 defines `pk(skX)` as either a computation or a lookup, and draft-ietf-lamps-pq-composite-kem specifies `tradPK` as an implicit input that is carried with the private key (see Section 4.3). A default implementation may support several known algorithms when the key is extractable.