Implement JSON dump conversion for torch_dtype in TrainingArguments (#31224)
* Implement JSON dump conversion for torch_dtype in TrainingArguments
* Add unit test for converting torch_dtype in TrainingArguments to JSON
* move unit test for converting torch_dtype into TrainerIntegrationTest class
* reformating using ruff
* convert dict_torch_dtype_to_str to private method _dict_torch_dtype_to_str
---------
Co-authored-by: jun.4 <jun.4@kakaobrain.com>