[Quantization] support pass MappingType for TorchAoConfig

[a120092009]

What does this PR do?

Passing MappingType for TorchAoConfig is invalid

 File "/workspace/volume/zty/diffusers/src/diffusers/configuration_utils.py", line 123, in register_to_config
logger.debug(f"Updating config from {previous_dict} to {internal_dict}")
^^^^^^^^^^^^^^^
File "/workspace/volume/zty/diffusers/src/diffusers/quantizers/quantization_config.py", line 671, in __repr__
return f"{self.__class__.__name__} {json.dumps(config_dict, indent=2, sort_keys=True)}\n"
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.12/json/__init__.py", line 238, in dumps
**kw).encode(obj)
^^^^^^^^^^^
File "/usr/lib/python3.12/json/encoder.py", line 202, in encode
chunks = list(chunks)
^^^^^^^^^^^^
File "/usr/lib/python3.12/json/encoder.py", line 432, in _iterencode
yield from _iterencode_dict(o, _current_indent_level)
File "/usr/lib/python3.12/json/encoder.py", line 406, in _iterencode_dict
yield from chunks
File "/usr/lib/python3.12/json/encoder.py", line 406, in _iterencode_dict
yield from chunks
File "/usr/lib/python3.12/json/encoder.py", line 439, in _iterencode
o = _default(o)
^^^^^^^^^^^
File "/usr/lib/python3.12/json/encoder.py", line 180, in default
raise TypeError(f'Object of type {o.__class__.__name__} '
TypeError: Object of type MappingType is not JSON serializable

Add JSON encoder for supporting MappingType

Test result:

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline?
• Did you read our philosophy doc (important for complex PRs)?
• Was this discussed/approved via a GitHub issue or the forum? Please add a link to it if that's the case. (Not related issue or PR yet)
• Did you make sure to update the documentation with your changes? Here are the
  documentation guidelines, and
  here are tips on formatting docstrings.
• Did you write any new necessary tests?

Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

[a120092009]

@a-r-r-o-w@dacorvo Could you guys take a look, thx :)

[a-r-r-o-w]

@bot /style

[github-actions]

Style fixes have been applied. View the workflow run here.

[a-r-r-o-w]

Thank you!

[a-r-r-o-w]

The update test is passing for me locally, thanks!