create a single util for formatting json

otherwise this can get out of sync across files
(e.g. our "hypos", "gold", "id", "lprobs", "num_unique" dictionary)

Look for files that currently format JSON, especially those using keys like 'hypos', 'gold', 'id', 'lprobs', 'num_unique'. Create a utility function in a central module (e.g., utils/json_utils.py) to handle consistent JSON formatting. Ensure all existing usages are updated to call this new utility. Run the project's tests to verify the refactor doesn't break anything.

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