Lazy import libraries in src/transformers/image_utils.py

[hmellor]

Lazy import the imports added by #34275.

Enables vllm-project/vllm#13905 (which strictly enforces that cv2 is lazily imported).

[HuggingFaceDocBuilderDev]

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[zucchini-nlp]

Makes sense to me since we use it only to load videos, and we're planning to separate away these fn to a new video_utils file

[ArthurZucker]

Yep thanks for protecting with requires backend! 🤗