[Main] [Refactor] Enable MoECommMethod in Eager Mode (#2791)

### What this PR does / why we need it?
1. Replace prepare/finalize operation in fused_moe.py by
moe_comm_method.prepare()/finalize()
2. Replace unified_fused_experts by moe_comm_method.fused_experts() in
fused_moe.py/w8a8_dynamic.py/w4a8_dynamic.py
3. Add calling _select_moe_comm_method in spec-decode proposers.
4. Currently, w4a8_dynamic does not support gatherep, use all2allv
instead.
5. Remove redundant code.
### Does this PR introduce _any_ user-facing change?
AllgatherEP switch is disabled in aclgraph/eager mode, just follow the
rules in modelrunner_v1._select_moe_comm_method()
### How was this patch tested?
e2e & ut


- vLLM version: v0.10.2
- vLLM main:
7f6f2c1182

Signed-off-by: Pr0Wh1teGivee <calvin_zhu0210@outlook.com>
Co-authored-by: weijinqian0 <12153182+weijinqian0@users.noreply.github.com>

vllm_ascend/ops/common_fused_moe.py

@@ -32,8 +32,8 @@ from vllm_ascend.ascend_config import get_ascend_config
 from vllm_ascend.distributed.parallel_state import get_mc2_group
 from vllm_ascend.ops.moe.experts_selector import select_experts
 from vllm_ascend.ops.moe.moe_comm_method import (AllGatherCommImpl,
-                                                 AlltoAllCommImpl, MC2CommImpl)
-from vllm_ascend.ops.moe.token_dispatcher import setup_token_dispatchers
+                                                 AlltoAllCommImpl, MC2CommImpl,
+                                                 NaiveMulticastCommImpl)
 from vllm_ascend.utils import ACL_FORMAT_FRACTAL_NZ, is_310p
 
 original_unquantized_fused_moe_init_func = UnquantizedFusedMoEMethod.__init__
@@ -280,17 +280,17 @@ class AscendFusedMoE(FusedMoE):
             num_redundant_experts,
             has_bias,
         )
-        setup_token_dispatchers(self.moe_config.ep_size,
-                                top_k=self.top_k,
-                                num_experts=self.global_num_experts,
-                                num_local_experts=self.local_num_experts)
+
         self.hidden_size = hidden_size
         self.moe_config.tp_group = get_tp_group()
         self.moe_config.dp_group = get_dp_group()
         self.moe_config.ep_group = get_ep_group()
         self.moe_config.mc2_group = get_mc2_group()
 
-        for method in {AllGatherCommImpl, AlltoAllCommImpl, MC2CommImpl}:
+        for method in {
+                AllGatherCommImpl, AlltoAllCommImpl, MC2CommImpl,
+                NaiveMulticastCommImpl
+        }:
             setattr(
                 self, method.__name__.lower(),
                 method(moe_config=self.moe_config))  # type: ignore[abstract]