Add Batch feature (XLS-56) (#5060)

- Specification: [XRPLF/XRPL-Standards 56](https://github.com/XRPLF/XRPL-Standards/blob/master/XLS-0056d-batch/README.md)
- Amendment: `Batch`
- Implements execution of multiple transactions within a single batch transaction with four execution modes: `tfAllOrNothing`, `tfOnlyOne`, `tfUntilFailure`, and `tfIndependent`.
- Enables atomic multi-party transactions where multiple accounts can participate in a single batch, with up to 8 inner transactions and 8 batch signers per batch transaction.
- Inner transactions use `tfInnerBatchTxn` flag with zero fees, no signature, and empty signing public key.
- Inner transactions are applied after the outer batch succeeds via the `applyBatchTransactions` function in apply.cpp.
- Network layer prevents relay of transactions with `tfInnerBatchTxn` flag - each peer applies inner transactions locally from the batch.
- Batch transactions are excluded from AccountDelegate permissions but inner transactions retain full delegation support.
- Metadata includes `ParentBatchID` linking inner transactions to their containing batch for traceability and auditing.
- Extended STTx with batch-specific signature verification methods and added protocol structures (`sfRawTransactions`, `sfBatchSigners`).

src/libxrpl/protocol/InnerObjectFormats.cpp

@@ -158,6 +158,13 @@ InnerObjectFormats::InnerObjectFormats()
     add(sfPermission.jsonName.c_str(),
         sfPermission.getCode(),
         {{sfPermissionValue, soeREQUIRED}});
+
+    add(sfBatchSigner.jsonName.c_str(),
+        sfBatchSigner.getCode(),
+        {{sfAccount, soeREQUIRED},
+         {sfSigningPubKey, soeOPTIONAL},
+         {sfTxnSignature, soeOPTIONAL},
+         {sfSigners, soeOPTIONAL}});
 }
 
 InnerObjectFormats const&