feat(sgl-kernel): add InfLLM v2 attention kernels (#29383)

Co-authored-by: Size Wang <paulgeorge13hhhhh@gmail.com>
Co-authored-by: lijiayi <lijiayi@modelbest.cn>
Co-authored-by: suhmily10 <suhmily@gmail.com>
Co-authored-by: Xiaoyue Xu <xiaoyue.xu.me@gmail.com>
Co-authored-by: hansjohn <74091612+hansjohn@users.noreply.github.com>
Co-authored-by: zhangyan <1762895426@qq.com>

sgl-kernel/python/sgl_kernel/__init__.py

@@ -71,6 +71,10 @@ else:
         shuffle_rows,
     )
     from sgl_kernel.grammar import apply_token_bitmask_inplace_cuda
+    from sgl_kernel.infllm_v2 import (
+        infllmv2_attn_stage1,
+        max_pooling_1d_varlen,
+    )
     from sgl_kernel.kvcacheio import (
         transfer_kv_all_layer,
         transfer_kv_all_layer_mla,