[Attention] Remove unused slot mapping from standard metadata

[9876543210-tc-0123456789]

Purpose

Related to #32335

Remove slot_mapping from standard attention metadata classes where KV cache updates have already been extracted into the separate do_kv_cache_update path.

This covers:

• FlashInfer
• FlexAttention
• TritonAttention
• RocmAttention

The test helper now passes CommonAttentionMetadata.slot_mapping directly to do_kv_cache_update, instead of reading it back from backend-specific metadata.

Tested:

• pytest tests/v1/attention/test_attention_backends.py

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[claude]

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[gemini-code-assist]

Code Review

This pull request refactors the attention metadata by removing the slot_mapping field from backend-specific metadata classes, including FlashInfer, Flex Attention, ROCm, and Triton. The slot_mapping is now accessed via common_attn_metadata in the test suite. I have no feedback to provide.

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @volcano303.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

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This pull request has been automatically marked as stale because it has not had any activity within 90 days. It will be automatically closed if no further activity occurs within 30 days. Leave a comment if you feel this pull request should remain open. Thank you!