- Add ``CamelModel`` pydantic model for use across libraries. This
  model allows for consistent camelCase JSON serialization, standarizing
  an expected format that can be used across ethereum python libraries.

- Add the ``OmitJsonSchema`` class to allow for the omission of excluded
  model fields from the JSON Schema representation.

- Since this is an acceptable model for JSON-RPC dicts, add this expectation
  into the ``apply_formatters_to_dict`` method, serializing the model fields
  into the JSON-RPC dicts before applying the formatter functions.

- Add tests for the CamelModel to ``apply_formatters_to_dict`` tests.

🩹 use `arg.get` in ``get_abi_input_names`` and ```get_abi_output_names``
📝 add newsfragment

* enhancement: add support for custom units

* test: add custom test case for unsupported unit in units dict

Co-authored-by: kclowes <kclowes@users.noreply.github.com>