Generate video outpaint code with WAN 2.1

[SlimRG]

What does this PR do?

This PR adds video_outpaint_wan21.py, a self-contained Python script demonstrating video outpainting using Alibaba Cloud's DashScope service and the WAN 2.1 VACE model (wan2.1-vace-plus).

The script:

• Submits an outpainting request to the DashScope API.
• Polls the asynchronous task for completion.
• Downloads the resulting outpainted video.

This provides a practical example for users to programmatically extend video frames.

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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• Did you write any new necessary tests?

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@sayakpaul @yiyixuxu

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