Refactor cache initialization and update composer config.

Extract cache adapter initialization into a separate method for clarity and reusability in `src/Injector.php`. Update `composer.json` to allow `bamarni/composer-bin-plugin` for improved plugin management during builds.

composer.json

@@ -81,5 +81,10 @@
         "phpmd": ["./vendor/bin/phpmd --exclude src/Annotation src text ./phpmd.xml"],
         "build": ["@cs", "@sa", "@pcov", "@metrics"],
         "compile": "./bin/bear.compile FakeVendor\\\\HelloWorld prod-app ./tests/Fake/fake-app"
+    },
+    "config": {
+        "allow-plugins": {
+            "bamarni/composer-bin-plugin": true
+        }
     }
 }

src/Injector.php

@@ -52,7 +52,7 @@ public static function getInstance(string $appName, string $context, string $app
         }
 
         $meta = new Meta($appName, $context, $appDir);
-        $cache = $cache ?? new ChainAdapter([new ApcuAdapter($injectorId), new FilesystemAdapter($injectorId, 0, $meta->tmpDir . '/injector')]);
+        $cache = self::getAdapter($cache, $injectorId, $meta);
         assert($cache instanceof AdapterInterface);
         /** @psalm-suppress all */
         [$injector, $fileUpdate] = $cache->getItem($injectorId)->get();
@@ -99,4 +99,17 @@ private static function factory(Meta $meta, string $context, ?AbstractModule $ov
 
         return $injector;
     }
+
+    public static function getAdapter(?CacheInterface $cache, string $injectorId, Meta $meta): CacheInterface
+    {
+        if ($cache instanceof CacheInterface) {
+            return $cache;
+        }
+        $filesystemAdapter = new FilesystemAdapter($injectorId, 0, $meta->tmpDir . '/injector');
+        if (ApcuAdapter::isSupported()) {
+            return new ChainAdapter([new ApcuAdapter($injectorId), $filesystemAdapter]);
+        }
+
+        return $filesystemAdapter;
+    }
 }