Attach specific `Model` objects to ingredients via `from_args`, enabling README examples

[parkervg]

We have the following example in the README:

Name	Image	Location	Area	Recreation Visitors (2022)	Description
Death Valley		California, Nevada	3,408,395.63 acres (13,793.3 km2)	1,128,862	Death Valley is the hottest, lowest, and driest place in the United States, with daytime temperatures that have exceeded 130 °F (54 °C).
Everglades		Alaska	7,523,897.45 acres (30,448.1 km2)	9,457	The country's northernmost park protects an expanse of pure wilderness in Alaska's Brooks Range and has no park facilities.
New River Gorge		West Virgina	7,021 acres (28.4 km2)	1,593,523	The New River Gorge is the deepest river gorge east of the Mississippi River.
Katmai		Alaska	3,674,529.33 acres (14,870.3 km2)	33,908	This park on the Alaska Peninsula protects the Valley of Ten Thousand Smokes, an ash flow formed by the 1912 eruption of Novarupta.

SELECT {{VQA('Describe this image.', 'parks::Image')}} FROM parks
    WHERE "Location" = 'Alaska'
    ORDER BY {{
        LLMMap(
            'Size in km2?',
            'parks::Area'
        )
    }} LIMIT 1

However, currently we only take one Model object via the blender arg:

blend(
    query=query,
    db=db, 
    blender=blender,
    ingredients={LLMQA, VQA}
)

Instead, we want the following pattern:

blend(
    query=query,
    db=db, 
    blender=text_model,
    ingredients={LLMQA, VQA.from_args(model=vqa_model)}
)

Where text_model is a text-based Model object, and vqa_model is a Model object that takes an image as an input.

For reference on the VQA model logic, see https://parkervg.github.io/blendsql/reference/examples/vqa-ingredient/

Acceptance Criteria

• VQA ingredient created
  • Should be in the blendsql/ingredients/builtin/vqa directory
  • The Program and QAIngredient model code can be adapted from the example above
• Add class method from_args to QAIngredient class, and add model: Model as a valid argument
  • See JoinIngredient for an example of this pattern
• Adapt end-to-end flow of blend.py to prioritize model passed via from_args(), but use blender=model as the default