Add plutus script support to the compatible transaction API

createCompatibleTx now takes a CompatibleTxBodyContent record with
per-input AnyWitness values, and computes spending redeemer pointers,
witness datums, the script integrity hash, collateral inputs,
transaction metadata and the validity upper bound. Witness indexing is
shared with the experimental transaction builder. Also export the
mkSpendingScriptDatum smart constructor from Cardano.Api.Experimental.

Author: carbolymer

.changes/20260807_cardano_api_compatible_plutus.yml

@@ -0,0 +1,8 @@
+project: cardano-api
+pr: 1282
+kind:
+  - feature
+  - breaking
+  - bugfix
+description: |
+  Add plutus spending script support to createCompatibleTx. Breaking: it now takes all transaction content as a single CompatibleTxBodyContent record and fails with the new CompatibleTxError. Export mkSpendingScriptDatum. Fix certificate and proposal script witnesses missing from the witness set, and proposal reference inputs being overwritten. Remove the redundant StakeCredential field from WitTxCert.