Handle array query parameters in list converters

PHP parses query strings like ?param[]=a&param[]=b as arrays.
RequestToListConverter and ArrayToListConverter now join array
values with comma before adding to RequestParameterList.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: maltehuebner

src/RequestParameterList/ArrayToListConverter.php

@@ -14,7 +14,11 @@ public static function convert(array $array): RequestParameterList
         $requestParameterList = new RequestParameterList();
 
         foreach ($array as $key => $value) {
-            $requestParameterList->add($key, $value);
+            if (is_array($value)) {
+                $value = implode(',', $value);
+            }
+
+            $requestParameterList->add($key, (string) $value);
         }
 
         return $requestParameterList;

src/RequestParameterList/RequestToListConverter.php

@@ -16,7 +16,11 @@ public static function convert(Request $request): RequestParameterList
         $requestParameterList = new RequestParameterList();
 
         foreach ($request->query->all() as $key => $value) {
-            $requestParameterList->add($key, $value);
+            if (is_array($value)) {
+                $value = implode(',', $value);
+            }
+
+            $requestParameterList->add($key, (string) $value);
         }
 
         return $requestParameterList;