[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>

benchmark/fla/benchmark_layernorm_gated.py

@@ -4,10 +4,10 @@ import numpy as np
 import torch
 
 # Import the function to benchmark
-from sglang.srt.layers.attention.fla.layernorm_gated import (
+from sglang.kernels.ops.attention.fla.layernorm_gated import (
     _layer_norm_fwd as layer_norm_fwd,
 )
-from sglang.srt.layers.attention.fla.layernorm_gated import (
+from sglang.kernels.ops.attention.fla.layernorm_gated import (
     rms_norm_ref,
 )