fix: Throw error when signing fails

cw_solana/lib/solana_client.dart

@@ -713,10 +713,13 @@ class SolanaWalletClient {
       transaction: transaction,
     );
 
-    sendTx() async => await sendTransaction(
-          serializedTransaction: serializedTransaction,
-          commitment: commitment,
-        );
+    sendTx() async {
+      await Future.delayed(const Duration(seconds: 2));
+      return await sendTransaction(
+        serializedTransaction: serializedTransaction,
+        commitment: commitment,
+      );
+    }
 
     final pendingTransaction = PendingSolanaTransaction(
       amount: inputAmount,
@@ -733,13 +736,18 @@ class SolanaWalletClient {
     required SolanaTransaction transaction,
   }) async {
     /// Sign the transaction with the owner's private key.
-    final ownerSignature = ownerPrivateKey.sign(transaction.serializeMessage());
-    transaction.addSignature(ownerPrivateKey.publicKey().toAddress(), ownerSignature);
+    try {
+      final ownerSignature = ownerPrivateKey.sign(transaction.serializeMessage());
+      transaction.addSignature(ownerPrivateKey.publicKey().toAddress(), ownerSignature);
 
-    /// Serialize the transaction.
-    final serializedTransaction = transaction.serializeString();
+      /// Serialize the transaction.
+      final serializedTransaction = transaction.serializeString();
 
-    return serializedTransaction;
+      return serializedTransaction;
+    } catch (e) {
+      printV(e);
+      throw Exception('Error signing transaction');
+    }
   }
 
   Future<String> sendTransaction({