[NPUW][VLM] Add support for multiple images for VLMs on NPU

[AlexanderKalistratov]

• Remove unnecessary assert
• Add test

[Copilot]

Pull request overview

This PR enables support for multiple images in VLM (Vision Language Model) pipelines when using NPU devices by removing an overly restrictive assertion that limited batch sizes to 1.

Key Changes:

• Removed the assertion that restricted NPU VLM pipelines to a single image/video
• Added a new test to verify multiple image support on NPU
• Simplified an existing test by removing unnecessary loop over multiple images

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/cpp/src/visual_language/pipeline.cpp	Removed assertion limiting NPU to single image/video processing
tests/python_tests/test_vlm_pipeline.py	Added test for multiple images, simplified existing test, and added missing platform skip decorator

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[Copilot]

The indentation of the ov_pipe.generate() call has changed from being inside a loop to standalone, but the indentation level appears inconsistent. The function call should be indented 4 spaces from the function definition, matching the style of other statements at the same level.