[Refactor]Refactor of vllm_ascend/distributed module (#5910)

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

### How was this patch tested?


- vLLM version: v0.13.0
- vLLM main:
11b6af5280

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

vllm_ascend/distributed/kv_transfer/__init__.py

@@ -41,5 +41,5 @@ def register_connector():
         "MooncakeLayerwiseConnector")
 
     KVConnectorFactory.register_connector(
-        "UCMConnector", "vllm_ascend.distributed.kv_transfer.ucm_connector",
+        "UCMConnector", "vllm_ascend.distributed.kv_transfer.kv_pool.ucm_connector",
         "UCMConnectorV1")