Fix java 25 compatibility

[ndr-brt]

Feature Request

Currently the code can't be built with java 25 (see)
Because of an issue caused by the new AsymmetricKey interface that has been put between Key and PublicKey and PrivateKey.

This is just a matter to cast the AsymmetricKey to Key to make it work in java 25, it will still work for java 17/21 (though the ide will tell that the cast is unnecessary).
PemParser:

            return keyPairList
                    .stream()
                    .filter(Objects::nonNull) // PEM strings that only contain public keys would get eliminated here
                    .map(keyPair -> keyPair.getPrivate() != null ? keyPair.getPrivate() : keyPair.getPublic())
                    .findFirst()
                    .map(Result::success)
                    .orElseGet(() -> Result.failure("PEM-encoded structure did not contain a private key."))
                    .map(Key.class::cast); // this is the change needed

Which Areas Would Be Affected?

e.g., DPF, CI, build, transfer, etc.

Why Is the Feature Desired?

Are there any requirements?

Who will sponsor this feature?

Please @-mention the committer that will sponsor your feature.

Solution Proposal

If possible, provide a (brief!) solution proposal.