add CI

.github/CODEOWNERS

@@ -0,0 +1 @@
+*   @apfelbox

.github/workflows/ci.yml

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+name: CI
+
+on: [ push ]
+
+jobs:
+    build-test:
+        runs-on: ubuntu-latest
+
+        strategy:
+            matrix:
+                php: ['8.3']
+
+        steps:
+            -   name: Checkout Code
+                uses: actions/checkout@v4
+
+            -   name: Setup PHP
+                uses: shivammathur/setup-php@v2
+                with:
+                    coverage: "none"
+                    ini-values: "memory_limit=-1"
+                    php-version: "${{ matrix.php }}"
+                    tools: "composer"
+
+            -   name: Display versions
+                run: |
+                    php --version
+                    php -r 'foreach (get_loaded_extensions() as $extension) echo $extension . " " . phpversion($extension) . PHP_EOL;'
+                    php -i
+
+            -   name: "Install Composer: Library / Composer Normalize"
+                run: composer install --optimize-autoloader --classmap-authoritative --no-interaction
+                working-directory: _init/library/vendor-bin/c-norm
+
+            -   name: "Install Composer: Library / PHP CS Fixer"
+                run: composer install --optimize-autoloader --classmap-authoritative --no-interaction
+                working-directory: _init/library/vendor-bin/cs-fixer
+
+            -   name: "Install Composer: Library / PHPStan"
+                run: composer install --optimize-autoloader --classmap-authoritative --no-interaction
+                working-directory: _init/library/vendor-bin/phpstan
+
+            -   name: "Install Composer: Symfony / Composer Normalize"
+                run: composer install --optimize-autoloader --classmap-authoritative --no-interaction
+                working-directory: _init/symfony/vendor-bin/c-norm
+
+            -   name: "Install Composer: Symfony / PHP CS Fixer"
+                run: composer install --optimize-autoloader --classmap-authoritative --no-interaction
+                working-directory: _init/symfony/vendor-bin/cs-fixer
+
+            -   name: "Install Composer: Symfony / PHPStan"
+                run: composer install --optimize-autoloader --classmap-authoritative --no-interaction
+                working-directory: _init/symfony/vendor-bin/phpstan