Convert CertState to a type family

[Lucsanszky]

Description

Checklist

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• Self-reviewed the diff

[lehins]

I did a quick skim over the PR and it looks awesome.
There is one important point that I made that will need to be address that has to do with a common issue of changes getting lost during rebasing, but that shouldn't be too hard.
I'll do a proper review once the PR is out of the Draft state.

[lehins]

For this PR this is totally fine, but just heads up for the future adjustments that we'll need to make we won't be able to construct it like that because VState will not be available.

This isn't really a problem since we can always construct it from an empty CertState, eg:

mkShelleyCertState pState dState = 
  def & certPStateL .~ pState
      & certDStateL .~ dState

mkConwayCertState pState dState vState = 
  mkConwayCertState pState dState & certVStateL .~ vState

Moreover in ledger rules we can always get away with modifying CertState, instead of constructing a new one.

Again, for this PR it will be fine to keep it as is, I am just giving you a heads up for the follow up work that we'll have to do.

[lehins]

Yeah, it will have to be concrete types that will be defining the Arbitrary instances, so feel free to get rid of this commented out code:

Suggested change

	-- instance Era era => Arbitrary (CertState era) where
	-- arbitrary = CertState <$> arbitrary <*> arbitrary <*> arbitrary
	-- shrink = genericShrink

[lehins]

It is good to add Impossible, cause this would result in a compile time error, since ByronEra does not have a EraCertState instance implemented

Suggested change

	upgradeCertState = error "It is not possible to translate Byron CertState with 'upgradeCertState'"
	upgradeCertState = error "Impossible: ByronEra does not have `EraCertState` instance"

[lehins]

Please take a look at the recent changes to all of the DecShareCBOR instances in this PR, since they have changed significantly since you started work on this work
See current instance for CertState:

cardano-ledger/libs/cardano-ledger-core/src/Cardano/Ledger/CertState.hs

Lines 423 to 439 in bc10beb

	instance Era era => DecShareCBOR (CertState era) where
	type
	Share (CertState era) =
	( Interns (Credential 'Staking)
	, Interns (KeyHash 'StakePool)
	, Interns (Credential 'DRepRole)
	, Interns (Credential 'HotCommitteeRole)
	)
	decSharePlusCBOR = decodeRecordNamedT "CertState" (const 3) $ do
	certVState <-
	decSharePlusLensCBOR $
	lens (\(cs, _, cd, ch) -> (cs, cd, ch)) (\(_, ks, _, _) (cs, cd, ch) -> (cs, ks, cd, ch))
	certPState <- decSharePlusLensCBOR _2
	certDState <-
	decSharePlusLensCBOR $
	lens (\(cs, ks, cd, _) -> (cs, ks, cd)) (\(_, _, _, ch) (cs, ks, cd) -> (cs, ks, cd, ch))
	pure CertState {certPState, certDState, certVState}

Please, make sure you don't loose any of the functionality from this PR: #4826