Consistent output shape from get_image_features

[zucchini-nlp]

What does this PR do?

as per title, branches off from #45783

The pooled image (OR video, NOT audio yet) feature output will now always satisfy three cond, where image features can be a list or a 3D tensor:

1. len(image_features) = len(input_images) # NOTE: or num_videos, not number of total video frames
2. image_features[0].ndim == 2
3. image_features[0].shape == {{actual seq length of this image, LM hidden size}}

Could make it complete BC and return the "correct" output when a certain flag is passed, but for now decided to update directly smaller utility fn in a breaking way

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[zucchini-nlp]

run-slow: aya_vision, cohere2_vision, deepseek_ocr2, gemma4, paddleocr_vl, qwen2_5_omni, qwen3_omni_moe

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Workflow Run ⚙️

This comment contains run-slow, running the specified jobs:

models: ["models/aya_vision", "models/cohere2_vision", "models/deepseek_ocr2", "models/gemma4", "models/paddleocr_vl", "models/qwen2_5_omni", "models/qwen3_omni_moe"]
quantizations: []

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Commit Info

Context	Commit	Description
RUN	5e5f7bbe	workflow commit (merge commit)
PR	52788433	branch commit (from PR)
main	b07d99be	base commit (on main)

✅ No failing test specific to this PR 🎉 👏 !

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[For maintainers] Suggested jobs to run (before merge)

run-slow: aya_vision, cohere2_vision, deepseek_ocr2, gemma4, paddleocr_vl, qwen2_5_omni, qwen3_omni_moe

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https://huggingface.co/spaces/transformers-community/circle-ci-viz?pr=46405&sha=80f4bb

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