refactor(core): enhance SDK structure and documentation

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

src/Data/Accounts/AccountData.php

@@ -0,0 +1,16 @@
+<?php
+
+namespace Apoloz\AlfaBank\Data\Accounts;
+
+use Spatie\LaravelData\Data;
+
+class AccountData extends Data
+{
+    public function __construct(
+        public string $number,
+        public string $dateCreated,
+        public string $type,
+        public ?string $mnemonic = null,
+        public ?array $balance = null, // Can be refined later with BalanceData
+    ) {}
+}