[Kernel] Relocate vendored fla and mamba kernel trees to sglang.kernels (RFC #29630, Phase 2.5, 7/7) (#30795)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

python/sglang/test/kits/attention_unittest/attention_methods/mamba2_attention.py

@@ -389,7 +389,7 @@ class MockMamba2ModelRunner(ModelRunner):
         # `MambaMixer2.forward_decode` requires. In production the
         # scheduler calls this during initialization; the fixture must
         # mirror that or DECODE crashes with a missing-backend error.
-        from sglang.srt.layers.attention.mamba.ops import (
+        from sglang.kernels.ops.mamba.triton_ops import (
             initialize_mamba_selective_state_update_backend,
         )