Check BLS PoP in PoolReg ledger rules

https://github.com/IntersectMBO/cardano-base/pull/693 checks proof of possession when building the `LeiosCommittee`. This function will be eventually used at times where we cannot easily report errors to the user (who is at fault), e.g. at the epoch boundary.

On top of those checks, we should check the proof of possession when (re-)registering pool with a BLS key set.

Ideally, this is also enforced by the `cardano-crypto-leios` (in `cardano-base` repo) API using a `ValidatedBLSKey` phantom type (or so).