[BugFix] Fix deepseek v3.2 mtp bug.

[whx-sjtu]

What this PR does / why we need it?

This PR fixes deepseek v3.2 mtp bug.

Does this PR introduce any user-facing change?

None

How was this patch tested?

All existed ci tests should pass.

• vLLM version: v0.11.0
• vLLM main: vllm-project/vllm@83f478b

[github-actions]

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[gemini-code-assist]

Code Review

This PR addresses a bug in the deepseek v3.2 mtp implementation by incorporating the DeepseekV32IndexerCache class and adjusting the logic for identifying attention layers in the draft model. The changes ensure that the indexer layers are correctly excluded from the draft attention layers, preventing potential errors during speculative decoding.