[Misc][Refactor] Add FusedMoERouter object (#30519)

Signed-off-by: Bill Nell <bnell@redhat.com>

vllm/model_executor/layers/quantization/fp8.py

@@ -29,6 +29,7 @@ from vllm.model_executor.layers.fused_moe.config import (
     FusedMoEQuantConfig,
     RoutingMethodType,
 )
+from vllm.model_executor.layers.fused_moe.fused_moe_router import FusedMoERouter
 from vllm.model_executor.layers.fused_moe.layer import UnquantizedFusedMoEMethod
 from vllm.model_executor.layers.fused_moe.oracle.fp8 import (
     Fp8MoeBackend,
@@ -997,6 +998,7 @@ class Fp8MoEMethod(FusedMoEMethodBase):
     def apply(
         self,
         layer: FusedMoE,
+        router: FusedMoERouter,
         x: torch.Tensor,
         router_logits: torch.Tensor,
     ) -> torch.Tensor | tuple[torch.Tensor, torch.Tensor]:
@@ -1051,7 +1053,7 @@ class Fp8MoEMethod(FusedMoEMethodBase):
                     apply_router_weight_on_input=layer.apply_router_weight_on_input,
                 )
 
-        topk_weights, topk_ids = layer.select_experts(
+        topk_weights, topk_ids = router.select_experts(
             hidden_states=x,
             router_logits=router_logits,
         )