Refactor body preparation into a separate method

Extract body preparation logic from main code block into a new `prepareBody` method. This enhances code readability and maintainability by isolating the responsibility and making the `EmbedInterceptor` class easier to extend and test.

src/EmbedInterceptor.php

@@ -66,20 +66,16 @@ private function embedResource(array $embeds, ResourceObject $ro, array $query):
                 $uri = uri_template($templateUri, $query);
                 /** @var Request $request */ // phpcs:ignore SlevomatCodingStandard.PHP.RequireExplicitAssertion.RequiredExplicitAssertion
                 $request = $this->resource->get->uri($uri);
-                if ($ro->body === null) {
-                    $ro->body = [];
-                }
-
-                if (! is_array($ro->body)) {
-                    throw new LinkException($embed->rel); // @codeCoverageIgnore
-                }
+                $this->prepareBody($ro, $embed);
 
                 if ($embed->rel === self::SELF_LINK) {
                     $this->linkSelf($request, $ro);
 
                     continue;
                 }
 
+                assert(is_array($ro->body));
+
                 $ro->body[$embed->rel] = clone $request;
             } catch (BadRequestException $e) {
                 // wrap ResourceNotFound or Uri exception
@@ -97,6 +93,17 @@ private function getFullUri(string $uri, ResourceObject $ro): string
         return $uri;
     }
 
+    public function prepareBody(ResourceObject $ro, Embed $embed): void
+    {
+        if ($ro->body === null) {
+            $ro->body = [];
+        }
+
+        if (! is_array($ro->body)) {
+            throw new LinkException($embed->rel); // @codeCoverageIgnore
+        }
+    }
+
     /** @return array<string, mixed> */
     private function getArgsByInvocation(MethodInvocation $invocation): array
     {