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/Pest.php

@@ -1,5 +1,9 @@
 <?php
 
+declare(strict_types=1);
+
+use Tests\TestCase;
+
 /*
 |--------------------------------------------------------------------------
 | Test Case
@@ -11,7 +15,7 @@
 |
 */
 
-pest()->extend(Tests\TestCase::class)
+pest()->extend(TestCase::class)
  // ->use(Illuminate\Foundation\Testing\RefreshDatabase::class)
     ->in('Feature');
 
@@ -26,9 +30,7 @@ pest()->extend(Tests\TestCase::class)
 |
 */
 
-expect()->extend('toBeOne', function () {
-    return $this->toBe(1);
-});
+expect()->extend('toBeOne', fn () => $this->toBe(1));
 
 /*
 |--------------------------------------------------------------------------
@@ -41,7 +43,7 @@ expect()->extend('toBeOne', function () {
 |
 */
 
-function something()
+function something(): void
 {
     // ..
 }