Fix NSA indexer nightly test failed issues

[Johnsonms]

Motivation

1. Fixed this issue [Bug] NSA indexer unit test test_indexer_with_different_topk fails #13296
2. Disable a test that's currently failing or unreliable due to accuracy
   alignment issues
3. Improve code formatting and style compliance in the test file

Modifications

• Fix test mock to dynamically compute max_kv_len from
  actual key tensor shape
• Update topk_transform signature with optional ks
  parameter
• Add missing Optional type hint import

Accuracy Tests

Benchmarking and Profiling

Checklist

• Format your code according to the Format code with pre-commit.
• Add unit tests according to the Run and add unit tests.
• Update documentation according to Write documentations.
• Provide accuracy and speed benchmark results according to Test the accuracy and Benchmark the speed.

[gemini-code-assist]

Summary of Changes

Hello @Johnsonms, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves critical compatibility issues within the NSA indexer, primarily by ensuring the RotaryEmbedding component correctly utilizes bfloat16 to avoid conflicts with vLLM's default fp32 behavior. Additionally, it significantly enhances the reliability of unit tests by making mock functions dynamically adapt to key tensor shapes, thereby preventing brittle test failures and improving overall code stability.

Highlights

• Rotary Embedding Dtype Fix: Explicitly set the dtype for RotaryEmbedding initialization within the NSA indexer to torch.bfloat16. This prevents potential fp32 default usage when integrating with vLLM, addressing a reported issue.
• Test Compatibility Enhancement: Improved test robustness by modifying the mock mqa_logits function to dynamically compute max_kv_len based on the actual key tensor shape (k_fp8.shape[0]), replacing a fixed value.
• Method Signature Update: Updated the topk_transform method signature in the test utilities to include an optional ks parameter (ks: Optional[torch.Tensor] = None).
• Type Hint Import: Added the missing Optional type hint import from the typing module in the test file for improved type checking.

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[gemini-code-assist]

Code Review

This pull request introduces several fixes for the NSA indexer, addressing dtype and test compatibility issues. The changes are well-motivated and correct. I have one suggestion to improve code clarity in one of the test mocks by using an underscore for an unused variable. Overall, this is a solid contribution.