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

database/migrations/0001_01_01_000001_create_cache_table.php

@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use Illuminate\Database\Migrations\Migration;
 use Illuminate\Database\Schema\Blueprint;
 use Illuminate\Support\Facades\Schema;
@@ -11,13 +13,13 @@ return new class extends Migration
      */
     public function up(): void
     {
-        Schema::create('cache', function (Blueprint $table) {
+        Schema::create('cache', function (Blueprint $table): void {
             $table->string('key')->primary();
             $table->mediumText('value');
             $table->integer('expiration');
         });
 
-        Schema::create('cache_locks', function (Blueprint $table) {
+        Schema::create('cache_locks', function (Blueprint $table): void {
             $table->string('key')->primary();
             $table->string('owner');
             $table->integer('expiration');