Improve the efficiency of verify_signed_data when verifying lots of data with a single key #504
Description
The verify_signed_data implementation for Rrsig in crate::validate takes a Dnskey converts that to the ring internal format and verifies the signature.
If the same Dnskey is used many times it might help to convert the key to ring internal format once and then use that to verify the signature.
For example for ldns-verify-zone.