[CI/CD] Add tests for encoding inputs

[oerc0122]

Currently no automated testing for JSONising structural formats.

At the moment, manual testing shows problems with saving the input parameters in the output files:

  File "MDANSE/Framework/Jobs/IJob.py", line 419, in run
    raise JobError(self, tb)
MDANSE.Framework.Jobs.IJob.JobError: Traceback (most recent call last):
  File "MDANSE/Framework/Jobs/IJob.py", line 412, in run
    self.finalize()
  File "MDANSE/Framework/Jobs/AngularCorrelation.py", line 213, in finalize
    self._outputData.write(
  File "MDANSE/Framework/OutputVariables/IOutputVariable.py", line 42, in write
    temp_format.write(basename, self, header, inputs)
  File "MDANSE/Framework/Formats/MDAFormat.py", line 64, in write
    HDFFormat.write(filename, data, header, run_instance, extension)
  File "MDANSE/Framework/Formats/HDFFormat.py", line 97, in write
    inputs = run_instance.output_configuration()
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "MDANSE/Framework/Configurable.py", line 209, in output_configuration
    result[name] = conf.to_json()
                   ^^^^^^^^^^^^^^
  File "MDANSE/Framework/Configurators/IConfigurator.py", line 263, in to_json
    return self._encoder.encode(self._original_input)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "[email protected]/3.11.9_1/Frameworks/Python.framework/Versions/3.11/lib/python3.11/json/encoder.py", line 200, in encode
    chunks = self.iterencode(o, _one_shot=True)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "[email protected]/3.11.9_1/Frameworks/Python.framework/Versions/3.11/lib/python3.11/json/encoder.py", line 258, in iterencode
    return _iterencode(o, 0)
           ^^^^^^^^^^^^^^^^^
  File "[email protected]/3.11.9_1/Frameworks/Python.framework/Versions/3.11/lib/python3.11/json/encoder.py", line 180, in default
    raise TypeError(f'Object of type {o.__class__.__name__} '
TypeError: Object of type PosixPath is not JSON serializable

Originally posted by @MBartkowiakSTFC in https://github.com/ISISNeutronMuon/MDANSE/issues/646#issuecomment-2634269887