What does this PR do?

Hello !

When working on Flux-Kontext, I discovered a silent bug regarding the resizing of the image, when calling the pipeline with several images.

• The__call__ method of theFluxKontextPipeline class takes animage of typeOptional[PipelineImageInput]. This variable can be a list in case of batch size > 1
• then theresize method of theVaeImageProcessor class is called (image = self.image_processor.resize(image, image_height, image_width)). But this method does not support lists as input. Due to the way this method is written (overriding theimage variable and then returning it), it doesn't resize the image and return it as-is.

In this fix, I corrected this by changing a minimal number of lines of code to handle lists. However, please let me know if you'd prefer that I also add additional input checks or safeguards.

Fixes # (issue)

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