[BUG] extract.ai acts up when columns already exist

[thomasstvr]

When an output column of extract.ai already exists, it affects the output of the extract. For example, by running the test below:

df = wrangles.recipe.run(
    """
    wrangles:
    - create.column:
        output: length
        value: 123
        
    - extract.ai:
        model: gpt-4o-mini
        api_key: ${OPENAI_API_KEY}
        seed: 1
        timeout: 60
        retries: 2
        output:
            length:
            type: string
            description: >-
                Any lengths found in the data
                such as cm, m, ft, etc.
    """,
    dataframe=pd.DataFrame({
        "data": [
            "wrench 25mm",
            "6m cable",
            "screwdriver 3mm"
        ],
    })
)

The output becomes:

Index	data	length
0	wrench 25mm	123
1	6m cable	6m
2	screwdriver 3mm	123

Instead of the expected:

Index	data	length
0	wrench 25mm	25mm
1	6m cable	6m
2	screwdriver 3mm	3mm