[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/worker/model_runner_v1.py

@@ -1663,7 +1663,8 @@ class NPUModelRunner(LoRAModelRunnerMixin):
             kv_connector_output=kv_connector_output,
         )
 
-    def _select_moe_comm_method(self, num_tokens: int) -> str:
+    def _select_moe_comm_method(self, num_tokens: int,
+                                with_prefill: bool) -> str:
         """1. If expert parallel is not enabled, we use all-gather since MC2 and all-to-all
         are designed for expert parallelism.
         2. If expert parallel is enabled, we need to consider the soc version and the
@@ -1687,6 +1688,8 @@ class NPUModelRunner(LoRAModelRunnerMixin):
             str: The selected MoE communication method, either "allgather", "mc2", or "alltoall".
         """
         soc_version = get_ascend_soc_version()
+        quant_type = getattr(self.vllm_config.model_config.hf_config,
+                             'moe_quantize', None)
 
         if not self.parallel_config.enable_expert_parallel:
             moe_comm_method = "allgather"
@@ -1694,12 +1697,19 @@ class NPUModelRunner(LoRAModelRunnerMixin):
             if num_tokens <= self.mc2_tokens_capacity and self.parallel_config.world_size_across_dp >= 16:
                 moe_comm_method = "mc2"
             else:
-                moe_comm_method = "allgather"
+                if quant_type == "w4a8_dynamic":
+                    moe_comm_method = "alltoall"
+                else:
+                    moe_comm_method = "allgather"
+
         elif soc_version in {AscendSocVersion.A3}:
             moe_comm_method = "mc2" if num_tokens <= self.mc2_tokens_capacity else "alltoall"
         else:
             raise ValueError(f"Unsupported soc_version: {soc_version}")
 
+        if moe_comm_method == "allgather" and with_prefill:
+            moe_comm_method = "naivemulticast"
+
         if is_global_first_rank():
             logger.debug(f"num_tokens: {num_tokens}, "
                          f"moe_comm_method: {moe_comm_method}")
@@ -1728,7 +1738,8 @@ class NPUModelRunner(LoRAModelRunnerMixin):
              intermediate_tensors) = (self._prepare_inputs(
                  scheduler_output, intermediate_tensors))
 
-        moe_comm_method = self._select_moe_comm_method(num_input_tokens)
+        moe_comm_method = self._select_moe_comm_method(num_input_tokens,
+                                                       self.with_prefill)
 
         batch_descriptor = BatchDescriptor(num_tokens=num_input_tokens,
                                            uniform_decode=False)
@@ -2100,7 +2111,8 @@ class NPUModelRunner(LoRAModelRunnerMixin):
         (num_tokens, num_tokens_across_dp, with_prefill,
          _) = self._sync_metadata_across_dp(num_tokens, with_prefill, False)
 
-        moe_comm_method = self._select_moe_comm_method(num_tokens)
+        moe_comm_method = self._select_moe_comm_method(num_tokens,
+                                                       with_prefill)
 
         # If cudagraph_mode.decode_mode() == FULL and
         # cudagraph_mode.seperate_routine(). This means that we are using