Add ops module ported from tzj/minference branch containing:
- xattn.py: XAttention block importance estimation with Triton kernels
- xattn_estimate(): standard estimation for sparse attention mask
- xattn_estimate_chunked(): chunked prefill compatible version
- flat_group_gemm_fuse_reshape(): fused stride reshape + GEMM kernel
- softmax_fuse_block_sum(): online softmax + block-wise sum kernel
- chunked_attention.py: Flash attention with LSE output for chunk merging
- test_xattn_estimate_chunked.py: verification test (all seq_lens pass)
This prepares the foundation for AttentionPolicy refactoring where
XAttentionPolicy.estimate() will call these ops.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
