feat: implement HeadQA

[chakravarthik27]

Harness setup:

harness = Harness(
    task="question-answering",
    model={
        "model": "gpt-4.1-mini",
        "hub": "openai"
    },
    data={
        'data_source': 'HeadQA',
    },
    config={
        "tests": {
            "defaults": {
                "min_pass_rate": 0.8
            },
            "robustness": {
                "add_ocr_typo": {"min_pass_rate": 0.8},
                "uppercase": {"min_pass_rate": 0.8},
                "add_speech_to_text_typo": {"min_pass_rate": 0.8}
            }
        }
    }
)

[blidiselalin]

Looks good.