feat: implement wallet and invoice factories, enhance wallet service methods, and add comprehensive tests

database/factories/WalletFactory.php

@@ -0,0 +1,27 @@
+<?php
+
+namespace Database\Factories;
+
+use App\Models\User;
+use Illuminate\Database\Eloquent\Factories\Factory;
+
+/**
+ * @extends \Illuminate\Database\Eloquent\Factories\Factory<\App\Models\Wallet>
+ */
+class WalletFactory extends Factory
+{
+    public function definition(): array
+    {
+        return [
+            'balance' => 0,
+            'user_id' => User::factory(),
+        ];
+    }
+
+    public function system(): static
+    {
+        return $this->state(fn (array $attributes) => [
+            'user_id' => null,
+        ]);
+    }
+}