Enable use of VRF batch verification crypto from Conway era onward

The crypto team has (re-)prepared newer versions of the VRF and KES algorithms/formats for use in eras after Babbage (ie starting with Conway after the Chang HF). This is materialised as three PI objectives that will involve Consensus:

1. VRF batch-compatibility (requires HF)
2. KES secure forgetting
3. KES signature size reduction (requires HF)

The goal of this issue is to implement batch VRF verification in consensus.

This implies:
* Adapting consensus to be able to use different crypto for VRF verification depending on the era
* Actually calling the batch VRF function from new crypto libraries