et_jsonizer: Refactor et_jsonizer

[TaekyungHeo]

Summary

Updated et_jsonizer for readability and maintainability.

Test Plan

$ pip install .
$ python3 -m chakra.et_jsonizer.et_jsonizer --input_filename ~/rank0.chakra --output_filename ~/rank0.chakra.json
$ tail ~/rank0.chakra.json
    {
      "name": "is_cpu_op",
      "int32Val": 0
    },
    {
      "name": "ts",
      "int64Val": "1697596710335517"
    }
  ]
}%               

[github-actions]

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