verification of ARC seal using ED25519 fails

Verifying an ARC seal with an Ed25519 key fails because the "special handling for RSA signatures" implemented in `Verifier.pm` is not applied in `ARC/Verifier.pm`, resulting in the error:
`Can't locate object method "size" via package "Crypt::PK::Ed25519" at /usr/local/libdata/perl5/site_perl/Mail/DKIM/ARC/Verifier.pm line 433.`