[Refactor] remove some metadata variables in attention_v1.

[weijinqian0]

RFC: #4629

Reason:

The metadata data class contains an excessive number of variables. We will inherit the metadata of the community and simultaneously remove some variables that are no longer needed at present.

Todo:

1. remove attn_state partly.

• vLLM version: v0.12.0
• vLLM main: vllm-project/vllm@ad32e3e

[gemini-code-assist]

Code Review

This pull request refactors attention metadata by removing several redundant variables like query_lens, query_start_loc_list, and is_only_prefill. The changes are mostly clean and improve code clarity. However, I found a critical issue where query_lens is re-calculated on-the-fly in xlite.py using attn_metadata.query_start_loc_cpu, but this attribute is not present in the AscendMetadata object, which will lead to a runtime error. I've provided a detailed comment with a suggested fix.

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[wjunLu]

I think those changes have not been tested, because there is no query_start_loc_cpu in AscendMetadata class.

But attn_metadata.query_start_loc_cpu is called, this will occur the following errors:

(EngineCore_DP0 pid=12553)   File "/vllm-workspace/vllm-ascend/vllm_ascend/xlite/xlite.py", line 260, in __call__
(EngineCore_DP0 pid=12553)     query_lens = attn_metadata.query_start_loc_cpu[
(EngineCore_DP0 pid=12553)                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
(EngineCore_DP0 pid=12553) AttributeError: 'AscendMetadata' object has no attribute 'query_start_loc_cpu'

Env:

• vllm: 0.13.0+empty
• vllm-ascend: 0.12.0rc2.dev138+g55beac9c9.d20251223