Add greedy verification kernel (#4383)

sgl-kernel/python/sgl_kernel/__init__.py

@@ -42,8 +42,13 @@ from sgl_kernel.sampling import (
     top_p_sampling_from_probs,
 )
 from sgl_kernel.speculative import (
-    build_tree_kernel,
     build_tree_kernel_efficient,
+    segment_packbits,
     tree_speculative_sampling_target_only,
+    verify_tree_greedy,
 )
 from sgl_kernel.version import __version__
+
+build_tree_kernel = (
+    None  # TODO(ying): remove this after updating the sglang python code.
+)