Ensure epochNo for BlsKey update is recorded correctly

Current implementation that was introduced in #6047 updates the epoch number in the StakePoolState regardless whether BLS key was updated or not.
We need to only update that value when bls key is different from the current bls key. Note that we do not need to look in to the future stake pool params, since that value will get replaced by the updated values from the certificate.

This doesn't mean that the Bls key was updated. It only means that something in StakePool params was updated. I believe we need to look into the old state and see if Bls key actually changed, before we can mark it as rotated.

This would probably be easier to do in the POOL rule instead, but I suggest we do it in a separate PR,once we have separate POOL rule defined for Dijkstra

_Originally posted by @lehins in https://github.com/IntersectMBO/cardano-ledger/pull/6047#discussion_r3937106008_

Start with the implementation introduced in #6047 and trace how StakePoolState handles the epoch number during a BLS key update. Read the relevant POOL rule discussion and compare the old state with the certificate’s updated values. Done means epochNo is recorded as rotated only when the BLS key actually differs, without looking into future stake pool parameters.

Written by the indexing model from the issue text.