rpc: add ChainHash message with both bytes and string representations

This commit introduces the `ChainHash` RPC message, which contains two
fields:
- A raw byte representation of the hash, ideal for direct use in
  Go RPC calls.
- A byte-reversed hexadecimal string representation of the hash,
  convenient for users who need to copy and paste the value, such as
  when passing it as a command-line argument.

rpcserver.go

@@ -3387,18 +3387,21 @@ func marshalOutboundParcel(
 
 	anchorTxHash := parcel.AnchorTx.TxHash()
 
-	// Marshal the anchor tx block hash.
-	var anchorTxBlockHashBytes []byte
+	// Marshal the anchor tx block hash into its RPC counterpart.
+	var anchorTxBlockHash *taprpc.ChainHash
 	parcel.AnchorTxBlockHash.WhenSome(func(hash chainhash.Hash) {
-		anchorTxBlockHashBytes = hash[:]
+		anchorTxBlockHash = &taprpc.ChainHash{
+			Hash:    hash[:],
+			HashStr: hash.String(),
+		}
 	})
 
 	return &taprpc.AssetTransfer{
 		TransferTimestamp:  parcel.TransferTime.Unix(),
 		AnchorTxHash:       anchorTxHash[:],
 		AnchorTxHeightHint: parcel.AnchorTxHeightHint,
 		AnchorTxChainFees:  parcel.ChainFees,
-		AnchorTxBlockHash:  anchorTxBlockHashBytes,
+		AnchorTxBlockHash:  anchorTxBlockHash,
 		Inputs:             rpcInputs,
 		Outputs:            rpcOutputs,
 	}, nil

taprpc/assetwalletrpc/assetwallet.swagger.json

@@ -895,9 +895,8 @@
           "description": "Describes the set of newly created asset outputs."
         },
         "anchor_tx_block_hash": {
-          "type": "string",
-          "format": "byte",
-          "description": "The block hash the contains the anchor transaction above. If unset, the\nanchor transaction is unconfirmed."
+          "$ref": "#/definitions/taprpcChainHash",
+          "description": "The block hash of the blockchain block that contains the anchor\ntransaction. If this value is unset, the anchor transaction is\nunconfirmed."
         }
       }
     },
@@ -910,6 +909,21 @@
       "default": "ASSET_VERSION_V0",
       "description": " - ASSET_VERSION_V0: ASSET_VERSION_V0 is the default asset version. This version will include\nthe witness vector in the leaf for a tap commitment.\n - ASSET_VERSION_V1: ASSET_VERSION_V1 is the asset version that leaves out the witness vector\nfrom the MS-SMT leaf encoding."
     },
+    "taprpcChainHash": {
+      "type": "object",
+      "properties": {
+        "hash": {
+          "type": "string",
+          "format": "byte",
+          "description": "The raw hash value in byte format.\n\nThis format is optimized for programmatic use, particularly for Go\ndevelopers, enabling easy integration with other RPC calls or binary\noperations."
+        },
+        "hash_str": {
+          "type": "string",
+          "description": "The byte-reversed hash value as a hexadecimal string.\n\nThis format is intended for human interaction, making it easy to copy,\npaste, and use in contexts like command-line arguments or configuration\nfiles."
+        }
+      },
+      "description": "ChainHash represents a hash value, typically a double SHA-256 of some data.\nCommon examples include block hashes and transaction hashes.\n\nThis versatile message type is used in various Bitcoin-related messages and\nstructures, providing two different formats of the same hash to accommodate\nboth developer and user needs."
+    },
     "taprpcKeyDescriptor": {
       "type": "object",
       "properties": {