[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/test_platform.py

@@ -461,7 +461,7 @@ class TestNPUPlatform(TestBase):
     def test_get_device_communicator_cls_returns_correct_value(self):
         self.assertEqual(
             self.platform.get_device_communicator_cls(),
-            "vllm_ascend.distributed.communicator.NPUCommunicator",
+            "vllm_ascend.distributed.device_communicators.npu_communicator.NPUCommunicator",
         )
 
     def test_is_pin_memory_available_returns_true(self):