refactor(api): migrate JSON instances to use Exp.IsEra constraints

Refactors JSON serialization instances for core types to use the experimental
Exp.IsEra constraint system instead of IsShelleyBasedEra/IsCardanoEra. This
unifies the constraint approach across the codebase and simplifies era-based
type class instances.

Key Changes:
- AddressInEra: Migrate ToJSON/FromJSON instances to Exp.IsEra
- ReferenceScript: Update JSON instances using Exp.convert for era witnesses
- TxOut (CtxTx/CtxUTxO): Consolidate era-specific parsing into unified handlers
- TxOutValue: Simplify FromJSON with direct era conversion

Implementation Details:
- Use Exp.useEra for obtaining era witnesses at the type level
- Convert era witnesses to required eon types (AlonzoEraOnwards, BabbageEraOnwards, etc.)
- Consolidate duplicate reconciliation logic into single reconcileDatums function
- Remove redundant era-specific pattern matching in favor of generic handlers

This refactoring maintains full backwards compatibility with existing JSON
formats while reducing code duplication and improving maintainability. The
changes prepare the codebase for easier extension to future eras by
centralizing era-handling logic.

Author: newhoggy

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

@@ -90,6 +90,7 @@ where
 
 import Cardano.Api.Byron.Internal.Key
 import Cardano.Api.Era
+import Cardano.Api.Experimental.Era qualified as Exp
 import Cardano.Api.HasTypeProxy
 import Cardano.Api.Key.Internal
 import Cardano.Api.Monad.Error
@@ -370,12 +371,14 @@ data AddressInEra era where
 instance NFData (AddressInEra era) where
   rnf (AddressInEra t a) = deepseq (deepseq t a) ()
 
-instance IsCardanoEra era => ToJSON (AddressInEra era) where
-  toJSON = Aeson.String . serialiseAddress
+instance Exp.IsEra era => ToJSON (AddressInEra era) where
+  toJSON =
+    Exp.obtainCommonConstraints (Exp.useEra @era) $
+      Aeson.String . serialiseAddress
 
-instance IsShelleyBasedEra era => FromJSON (AddressInEra era) where
+instance Exp.IsEra era => FromJSON (AddressInEra era) where
   parseJSON =
-    let sbe = shelleyBasedEra @era
+    let sbe = convert (Exp.useEra @era)
      in withText "AddressInEra" $ \txt -> do
           addressAny <- P.runParserFail parseAddressAny txt
           pure $ anyAddressInShelleyBasedEra sbe addressAny

cardano-api/src/Cardano/Api/Plutus/Internal/Script.hs

@@ -125,6 +125,7 @@ import Cardano.Api.Era.Internal.Core
 import Cardano.Api.Era.Internal.Eon.BabbageEraOnwards
 import Cardano.Api.Era.Internal.Eon.ShelleyBasedEra
 import Cardano.Api.Error
+import Cardano.Api.Experimental.Era qualified as Exp
 import Cardano.Api.HasTypeProxy
 import Cardano.Api.Hash
 import Cardano.Api.Key.Internal
@@ -1647,16 +1648,14 @@ deriving instance Eq (ReferenceScript era)
 
 deriving instance Show (ReferenceScript era)
 
-instance IsCardanoEra era => ToJSON (ReferenceScript era) where
+instance Exp.IsEra era => ToJSON (ReferenceScript era) where
   toJSON (ReferenceScript _ s) = object ["referenceScript" .= s]
   toJSON ReferenceScriptNone = Aeson.Null
 
-instance IsCardanoEra era => FromJSON (ReferenceScript era) where
+instance Exp.IsEra era => FromJSON (ReferenceScript era) where
   parseJSON = Aeson.withObject "ReferenceScript" $ \o ->
-    caseByronToAlonzoOrBabbageEraOnwards
-      (const (pure ReferenceScriptNone))
-      (\w -> ReferenceScript w <$> o .: "referenceScript")
-      (cardanoEra :: CardanoEra era)
+    let w = Exp.convert (Exp.useEra @era)
+     in ReferenceScript w <$> o .: "referenceScript"
 
 refScriptToShelleyScript
   :: ShelleyBasedEra era