args JSON serialize issue when using PickleEncoder

[huubbouma]

Very similar to issue #135 when an object in the kwargs was giving issues.
In another (old django project) I migrated from django-rq and I used the PickleEncoder

Now the args in the message_dict is the cause of the problem. In #135 it was the kwargs

(in my case a MediationRequest object)

  File "/home/huub/projects/demo/django_dramatiq/django_dramatiq/admin.py", line 48, in message_details
    message_details = json.dumps(message_dict, indent=4)
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/huub/.pyenv/versions/3.12.9/lib/python3.12/json/__init__.py", line 238, in dumps
    **kw).encode(obj)
          ^^^^^^^^^^^
  File "/home/huub/.pyenv/versions/3.12.9/lib/python3.12/json/encoder.py", line 202, in encode
    chunks = list(chunks)
             ^^^^^^^^^^^^
  File "/home/huub/.pyenv/versions/3.12.9/lib/python3.12/json/encoder.py", line 432, in _iterencode
    yield from _iterencode_dict(o, _current_indent_level)
  File "/home/huub/.pyenv/versions/3.12.9/lib/python3.12/json/encoder.py", line 406, in _iterencode_dict
    yield from chunks
  File "/home/huub/.pyenv/versions/3.12.9/lib/python3.12/json/encoder.py", line 326, in _iterencode_list
    yield from chunks
  File "/home/huub/.pyenv/versions/3.12.9/lib/python3.12/json/encoder.py", line 439, in _iterencode
    o = _default(o)
        ^^^^^^^^^^^
  File "/home/huub/.pyenv/versions/3.12.9/lib/python3.12/json/encoder.py", line 180, in default
    raise TypeError(f'Object of type {o.__class__.__name__} '
TypeError: Object of type MediationRequest is not JSON serializable