[BUGFIX] fix Attention import path

[xuechendi]

Purpose

The Attention/MLAAttention path used in #32133 is out of date.

Trigger bug on below test

pytest -v -s v1/structured_output/test_backend_guidance.py

error log:

File "/usr/local/lib/python3.12/dist-packages/vllm/model_executor/model_loader/utils.py", line 21, in <module>
ERROR 01-30 16:28:14 [registry.py:798]     from vllm.model_executor.model_loader.reload import (
ERROR 01-30 16:28:14 [registry.py:798]   File "/usr/local/lib/python3.12/dist-packages/vllm/model_executor/model_loader/reload/__init__.py", line 29, in <module>
ERROR 01-30 16:28:14 [registry.py:798]     from .layerwise import (
ERROR 01-30 16:28:14 [registry.py:798]   File "/usr/local/lib/python3.12/dist-packages/vllm/model_executor/model_loader/reload/layerwise.py", line 10, in <module>
ERROR 01-30 16:28:14 [registry.py:798]     from vllm.attention.layer import Attention, MLAAttention
ERROR 01-30 16:28:14 [registry.py:798] ModuleNotFoundError: No module named 'vllm.attention'

This PR is to fix this issue

Test Plan

pytest -v -s v1/structured_output/test_backend_guidance.py

Test Result

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• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
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• (Optional) Release notes update. If your change is user facing, please update the release notes draft in the Google Doc.

[gemini-code-assist]

Code Review

This pull request correctly fixes a ModuleNotFoundError by updating the import path for Attention and MLAAttention. The change is straightforward and also improves import ordering. I have no further suggestions.

[mgoin]

Thanks for the help @xuechendi! I will close this to prioritize #33432 since it was posted before