refactor: allow HelloResponseInterface methods to return framework-specific response objects

- Changed json() and render() return types from string to mixed
- Updated docblocks to reflect flexible return type
- Enables implementations to return framework-native response objects
  (e.g. Drupal JsonResponse, HtmlResponse, TrustedRedirectResponse)

Author: UnnikrishnanBhargavakurup

src/HelloResponse/HelloResponseInterface.php

@@ -83,9 +83,9 @@ public function redirect(string $url);
      * for encoding and returning JSON data.
      *
      * @param array<string, mixed> $data The data to be converted to a JSON response.
-     * @return string The string encoded JSON response data.
+     * @return mixed
      */
-    public function json(array $data): string;
+    public function json(array $data);
 
     /**
      * Renders the given content as an HTTP response.
@@ -95,7 +95,7 @@ public function json(array $data): string;
      * depending on the framework or environment being used.
      *
      * @param string $content The content to render as a response.
-     * @return string The rendered response content.
+     * @return mixed
      */
-    public function render(string $content): string;
+    public function render(string $content);
 }