[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>

examples/disaggregated_prefill_v1/mooncake_connector_deployment_guide.md

@@ -55,7 +55,6 @@ vllm serve "/xxxxx/DeepSeek-V2-Lite-Chat" \
   "kv_port": "20001",
   "engine_id": "0",
   "kv_rank": 0,
-  "kv_connector_module_path": "vllm_ascend.distributed.mooncake_connector",
   "kv_connector_extra_config": {
             "prefill": {
                     "dp_size": 2,
@@ -123,7 +122,6 @@ vllm serve "/xxxxx/DeepSeek-V2-Lite-Chat" \
   "kv_port": "20002",
   "engine_id": "1",
   "kv_rank": 1,
-  "kv_connector_module_path": "vllm_ascend.distributed.mooncake_connector",
   "kv_connector_extra_config": {
             "prefill": {
                     "dp_size": 2,

examples/offline_disaggregated_prefill_npu.py

@@ -56,7 +56,6 @@ def run_prefill(prefill_done, process_close):
         kv_role="kv_producer",
         kv_port="30000",
         engine_id="0",
-        kv_connector_module_path="vllm_ascend.distributed.mooncake_connector",
         kv_connector_extra_config={"prefill": {"dp_size": 1, "tp_size": 1}, "decode": {"dp_size": 1, "tp_size": 1}},
     )
     # Set NPU memory utilization to 0.8
@@ -104,7 +103,6 @@ def run_decode(prefill_done):
         kv_role="kv_consumer",
         kv_port="30100",
         engine_id="1",
-        kv_connector_module_path="vllm_ascend.distributed.mooncake_connector",
         kv_connector_extra_config={"prefill": {"dp_size": 1, "tp_size": 1}, "decode": {"dp_size": 1, "tp_size": 1}},
     )