Generate video outpaint code with WAN 2.1

[SlimRG]

Add WAN 2.1 Video Outpaint Examples

This PR introduces comprehensive examples for performing video outpaint using the WAN 2.1 model. Video outpaint allows users to extend the boundaries of an existing video (left, right, top, or bottom) and fill the newly created regions with AI-generated content, ensuring temporal consistency with the original footage.

The examples include:

• wan_video_outpaint.py: A full-featured pipeline with a command-line interface for flexible outpainting.
• wan_video_outpaint_simple.py: A simplified demo script for quick testing and understanding.
• Supporting files: requirements_wan_outpaint.txt, README_wan_video_outpaint.md (detailed usage and tips), and test_wan_outpaint.py.

This enables users to easily expand video scenes, add context, or change aspect ratios while leveraging WAN 2.1's capabilities for high-quality, temporally consistent generation.

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