[EPLB] Reduce the memory used for batch_isend_irecv (#7344)

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

#6729 seems to reduce the NPU memory usage of eplb, but actually moves
the buffer allocation of dist.all_gather_into_tensor to
dist.batch_isend_irecv. Therefore, the overall NPU memory usage is not
reduced. This PR completely reduces the memory usage in this part.
### Does this PR introduce _any_ user-facing change?

### How was this patch tested?
Remaining memory of each rank before the repair.
<img width="649" height="99" alt="image"
src="https://github.com/user-attachments/assets/52a67592-e0e8-4f9a-b194-b84cb848c598"
/>

Remaining memory of each rank after the repair.
<img width="641" height="99" alt="image"
src="https://github.com/user-attachments/assets/0bc2e67c-f328-4dea-98af-d7a459fb4876"
/>

Close EPLB.
<img width="543" height="45" alt="image"
src="https://github.com/user-attachments/assets/6dcba19d-4401-44b8-a6d3-c7b35ee983c7"
/>

Memory of weights for each rank.
<img width="648" height="46" alt="image"
src="https://github.com/user-attachments/assets/4db2fd04-98a0-4d26-a026-2e8287102b99"
/>

Estimated memory for EPLB: 15.68  / 48 (layer_num) + 2 * 0.02 = 0.35 GB


- vLLM version: v0.17.0
- vLLM main:
4034c3d32e

Signed-off-by: shenchuxiaofugui <1311027364@qq.com>

vllm_ascend/eplb/eplb_updator.py

@@ -155,12 +155,12 @@ class EplbUpdator:
         for dst_rank in range(self.world_size):
             if dst_rank == self.rank_id:
                 continue
-            comm_op_list.append(dist.P2POp(dist.isend, src_tensor, dst_rank))
+            comm_op_list.append(dist.P2POp(dist.isend, src_tensor, dst_rank, group=self.comm_group.device_group))
 
         for src_rank in range(self.world_size):
             if src_rank == self.rank_id:
                 continue
-            comm_op_list.append(dist.P2POp(dist.irecv, src_tensor, src_rank))
+            comm_op_list.append(dist.P2POp(dist.irecv, src_tensor, src_rank, group=self.comm_group.device_group))
         if comm_op_list:
             reqs = dist.batch_isend_irecv(comm_op_list)