[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>

vllm_ascend/platform.py

@@ -411,7 +411,7 @@ class NPUPlatform(Platform):
 
     @classmethod
     def get_device_communicator_cls(cls) -> str:
-        return "vllm_ascend.distributed.communicator.NPUCommunicator"
+        return "vllm_ascend.distributed.device_communicators.npu_communicator.NPUCommunicator"
 
     @classmethod
     def is_pin_memory_available(cls):