code: public function withAddedHeaders(array $headers)
      {
          $object = clone $this;
          $object->inProcessingLoop = false;
          $object->configs['headers'] = [];
          foreach ($headers as $keyName => $value) {
              $keyName = $this->normalizeHeaderName($keyName);
              if (!$keyName) {
                  continue;
              }
  
              if (!isset($this->configs['headers'])) {
                  $object->configs['headers'] = [];
              }
  
              $object->configs['headers'][$keyName] = !is_array($value) ? [$value] : $value;
              $object->request = $object->request->withAddedHeader($keyName, $value);
          }
  
          return $object->buildConfigClient();
      }
docs: With Added Current Headers
  
  @param array $headers
  @return static