please add strength to wanimagetovideopipeline

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i use wanimagetovideopipeline and works fine. now i switch to lightx2v lora and use 4steps. the video just horner the original image and seems ignore the prompt. could you add strength like that in videotovideo？
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Start by locating the WanImageToVideoPipeline entry point and comparing the requested strength behavior with the existing video-to-video path. Reproduce the four-step LightX2V LoRA case described in the issue, then define and verify what strength should change; the work is done when the prompt is no longer ignored and the behavior is covered by appropriate tests.

Written by the indexing model from the issue text.