[bugfix] Fix dummy-run and multi-node issues in MoE routing and MTP (#4947)

### What this PR does / why we need it?

- Fix a premature `return` in `moe_init_routing_quant_v2.cpp` so the
routing kernel completes correctly instead of exiting early in certain
paths.
- Switch `FusedAlltoAllCommImpl` to use the MC2-based token dispatcher
and prepare/finalize routines, aligning MoE communication with the MC2
algorithm optimized for Ascend devices.
- Add a temporary override in `MtpProposer` to map `FUSED_ALLTOALL` back
to `ALLTOALL` until the MoE communication type selection logic is fully
finalized, avoiding incorrect behavior in dummy-run flows.
- Simplify the MoE communication selection for Ascend 910-93 in
`NPUModelRunner` by removing the EP-size guard on `FUSED_ALLTOALL`,
which fixes failures in multi-node / larger-EP configurations while
keeping MC2 routing under the configured token capacity.

- vLLM version: v0.12.0
- vLLM main:
ad32e3e19c

Signed-off-by: mojave2 <chenchen145@huawei.com>

csrc/dispatch_ffn_combine/op_kernel/moe_init_routing_quant_v2/moe_init_routing_quant_v2.cpp

@@ -114,7 +114,6 @@ __aicore__ inline  void moe_init_routing_quant_v2(
       srcToDstAndGatherOp.Init(x, scale, expandedRowIdx, expandedX, dynamicQuantScale, workspace, tilingData, &srcToDstGatherPipe);
       srcToDstAndGatherOp.Process();
       srcToDstGatherPipe.Destroy();
-      return;
     }
   }