text: Title: possible to escape already jsonified string ?
  Body: I am working with pandas objects that have a very fast to_json() method to serialise pandas.Series.
  I need to serialize a dict with some elements which are pandas objects, e.g.:
  `{ "data": pandas.Series(...) }`
  I would like to be able to transform the dict as
  `{ "data": SerializedJSON("[1,3,4, ...]") }`
  with
  ```
  class SerializedJSON(str):
      """An object of type SerializedJSON is a string that will be injected as such in the finale JSON string"""
      pass
  ```
  so that orjson would not escape again this string.
  
  Does this make sense ? Would it be useful to add this SerializedJSON ?
  