[Refactor]Refactor of vllm_ascend/distributed module (#5719)

### What this PR does / why we need it?
Based on the RFC:https://github.com/vllm-project/vllm-ascend/issues/5604

This PR is a refactoring of vllm_ascend/distributed, moving all
kv_transfer realtaed codes into a dedicated folder, which has already
been done in vLLM

### Does this PR introduce _any_ user-facing change?
NA

### How was this patch tested?


- vLLM version: v0.13.0
- vLLM main:
2f4e6548ef

---------

Signed-off-by: lty <linhebiwen@gmail.com>

tests/ut/distributed/test_communicator.py

@@ -4,7 +4,8 @@ from unittest.mock import MagicMock, patch
 import torch
 import torch.distributed as dist
 
-from vllm_ascend.distributed.communicator import NPUCommunicator
+from vllm_ascend.distributed.device_communicators.npu_communicator import \
+    NPUCommunicator
 
 
 class TestNPUCommunicator(unittest.TestCase):