[Multi Modal] Update multimodal_manager to align with vllm changes

[kwang3939]

Description

gather_mm_placeholders and scatter_mm_placeholders are deprecated by vllm: vllm-project/vllm#33362.
Update the multimodal_manager to align with the changes.
Pin the vllm version right to this deprecation commit. There are some other errors when using the latest vllm version.

Tests

Tested locally with:

pytest -v -s tests/runner/test_multimodal_manager.py
bash tests/e2e/benchmarking/mm_bench.sh

Checklist

Before submitting this PR, please make sure:

• I have performed a self-review of my code.
• I have necessary comments in my code, particularly in hard-to-understand areas.
• I have made or will make corresponding changes to any relevant documentation.

[github-actions]

Description

Start with a short description of what the PR does and how this is a change from
the past.

The rest of the description includes relevant details and context, examples:

• why is this change being made,
• the problem being solved and any relevant context,
• why this is a good solution,
• some information about the specific implementation,
• shortcomings of the solution and possible future improvements.

If the change fixes a Github issue, please include a link, e.g.,:
FIXES: #123456

Tests

Please describe how you tested this change, and include any instructions and/or
commands to reproduce.

Checklist

Before submitting this PR, please make sure:

• I have performed a self-review of my code.
• I have necessary comments in my code, particularly in hard-to-understand areas.
• I have made or will make corresponding changes to any relevant documentation.