Make Blockchain Subscribe methods return Unsubscribe callback

packages/stack/src/blockchain/base-blockchain.ts

@@ -4,6 +4,7 @@ import {
   type BlockchainCallback,
   type BlockchainUTXOs,
   type BlockchainTransactions,
+  type BlockchainUnsubscribeCallback,
 } from './types.js';
 
 import { Transaction } from '@xocash/primitives';
@@ -109,7 +110,7 @@ export abstract class BaseBlockchain<
   abstract subscribeLockscript(
     lockscript: string | Uint8Array,
     callback: BlockchainCallback<AddressNotificationPayload>,
-  ): Promise<void>;
+  ): Promise<BlockchainUnsubscribeCallback>;
 
   /**
    * Removes a subscription for a specific blockchain address.
@@ -136,7 +137,7 @@ export abstract class BaseBlockchain<
   abstract subscribeAddress(
     address: string,
     callback: BlockchainCallback<AddressNotificationPayload>,
-  ): Promise<void>;
+  ): Promise<BlockchainUnsubscribeCallback>;
 
   /**
    * Removes a subscription for a specific blockchain address.
@@ -163,7 +164,7 @@ export abstract class BaseBlockchain<
   abstract subscribeTransaction(
     transactionHash: string,
     callback: BlockchainCallback<TransactionNotificationPayload>,
-  ): Promise<void>;
+  ): Promise<BlockchainUnsubscribeCallback>;
 
   /**
    * Removes a subscription for a specific transaction.