chore: add GitHub Actions CI workflow

.github/workflows/ci.yml

@@ -0,0 +1,45 @@
+name: CI
+
+on:
+  push:
+    branches: [ master, main ]
+  pull_request:
+    branches: [ master, main ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v3
+
+    - name: Setup PHP
+      uses: shivammathur/setup-php@v2
+      with:
+        php-version: '8.2'
+        extensions: mbstring, intl
+        coverage: xdebug
+
+    - name: Validate composer.json and composer.lock
+      run: composer validate --strict
+
+    - name: Cache Composer packages
+      id: composer-cache
+      uses: actions/cache@v3
+      with:
+        path: vendor
+        key: ${{ runner.os }}-php-${{ hashFiles('**/composer.lock') }}
+        restore-keys: |
+          ${{ runner.os }}-php-
+
+    - name: Install dependencies
+      run: composer install --prefer-dist --no-progress
+
+    - name: Run test suite
+      run: vendor/bin/phpunit --coverage-text
+
+    - name: Run Static Analysis (PHPStan)
+      run: vendor/bin/phpstan analyse src --level 5
+
+    - name: Check Code Style (PHP_CodeSniffer)
+      run: vendor/bin/phpcs --standard=PSR12 src