chore: Update vllm_engine.py to support vllm version >= 0.5.1

[T-Atlas]

What does this PR do?

Minimizes modifications to adapt to changes in vllm version 0.5.1 and later (regarding vllm-project/vllm#5852).

Fixes addresses the error encountered when starting the web UI:

vllm_engine.py, line 33, in <module>
    from vllm.multimodal.image import ImagePixelData
ImportError: cannot import name 'ImagePixelData' from 'vllm.multimodal.image'

Specific Changes Made

• File: vllm_engine.py
  • Updated the import statement for ImagePixelData to handle changes in vllm version 0.5.1 and later.
  • Introduced a conditional import to ensure compatibility with versions greater than 0.5.1 and 0.5.0.
  • Updated the logic to handle ImagePixelData and MultiModalData correctly based on the vllm version.

Before submitting

• [ ✓ ] Did you read the contributor guideline?
• Did you write any new necessary tests?

[hiyouga]

LGTM!