feat: integrate PHPStan, Rector and Pint code quality tools (#13)

* feat: integrate PHPStan, Rector and Pint code quality tools

- Add larastan, rector, and rector-laravel dev dependencies
- Configure PHPStan at max level with Larastan extension
- Configure Rector with Laravel sets and code quality rules
- Configure Pint with strict rules (final_class, strict_types)
- Add composer scripts: lint, test:lint, test:types, test:unit
- Add GitHub Actions workflow for CI on push/PR
- Apply code style fixes across all files

* docs: add code quality section to README

tests/Unit/ExampleTest.php

@@ -1,10 +1,12 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Tests\Unit;
 
 use PHPUnit\Framework\TestCase;
 
-class ExampleTest extends TestCase
+final class ExampleTest extends TestCase
 {
     /**
      * A basic test example.