Refactor DPP script

[rafvasq]

Refactors the DPP script primarily to improve code structure and readability.

• General organization and consolidation
• Use of helper functions for logic like getting valid_prompts and separate types of tests (metric, token, etc.)
• Separates AIU and CPU validation generation

[prashantgupta24]

Worth putting a main function too so that we can do something like this?

if __name__ == "__main__":
    main()

That might simplify this too: https://github.com/foundation-model-stack/aiu-fms-testing-utils/blob/main/pyproject.toml#L49

[prashantgupta24]

Also worth checking if the above changes affect the project.scripts: https://github.com/foundation-model-stack/aiu-fms-testing-utils/blob/main/pyproject.toml#L49