refactor(api): export caseBabbageOnlyOrConwayEraOnwards from public API

Completes the integration of caseBabbageOnlyOrConwayEraOnwards by adding it
to the public API exports, ensuring it's available alongside other era case
functions like caseByronOrShelleyBasedEra.

- Add caseBabbageOnlyOrConwayEraOnwards to Cardano.Api.Era export list
- Create new "Case on BabbageEraOnwards" subsection for organization
- Add corresponding export section in Internal.Case module
- Implement the function to handle Babbage-only vs Conway+ era branching

The function enables cleaner conditional logic when dealing with features
that differ between Babbage and Conway eras, particularly useful for
handling Conway-specific governance features and protocol parameters.

Author: newhoggy

cardano-api/src/Cardano/Api/Era.hs

@@ -74,6 +74,9 @@ module Cardano.Api.Era
   , caseShelleyToMaryOrAlonzoEraOnwards
   , caseShelleyToAlonzoOrBabbageEraOnwards
   , caseShelleyToBabbageOrConwayEraOnwards
+
+    -- ** Case on BabbageEraOnwards
+  , caseBabbageOnlyOrConwayEraOnwards
   )
 where
 

cardano-api/src/Cardano/Api/Era/Internal/Case.hs

@@ -13,6 +13,8 @@ module Cardano.Api.Era.Internal.Case
   , caseShelleyToMaryOrAlonzoEraOnwards
   , caseShelleyToAlonzoOrBabbageEraOnwards
   , caseShelleyToBabbageOrConwayEraOnwards
+  -- Case on BabbageEraOnwards
+  , caseBabbageOnlyOrConwayEraOnwards
   -- Conversions
   , shelleyToAlonzoEraToShelleyToBabbageEra
   , alonzoEraOnwardsToMaryEraOnwards
@@ -157,6 +159,19 @@ caseShelleyToBabbageOrConwayEraOnwards l r = \case
   ShelleyBasedEraConway -> r ConwayEraOnwardsConway
   ShelleyBasedEraDijkstra -> error "caseShelleyToBabbageOrConwayEraOnwards: DijkstraEra is not supported"
 
+-- | @caseBabbageOnlyOrConwayEraOnwards f g era@ applies @f@ to babbage era only;
+-- and applies @g@ to conway and later eras.
+caseBabbageOnlyOrConwayEraOnwards
+  :: ()
+  => a
+  -> (ConwayEraOnwardsConstraints era => ConwayEraOnwards era -> a)
+  -> BabbageEraOnwards era
+  -> a
+caseBabbageOnlyOrConwayEraOnwards l r = \case
+  BabbageEraOnwardsBabbage -> l
+  BabbageEraOnwardsConway -> r ConwayEraOnwardsConway
+  BabbageEraOnwardsDijkstra -> error "caseBabbageOnlyOrConwayEraOnwards: DijkstraEra is not supported"
+
 {-# DEPRECATED shelleyToAlonzoEraToShelleyToBabbageEra "Use convert instead" #-}
 shelleyToAlonzoEraToShelleyToBabbageEra
   :: ()