[KVCache][Scheduler] disable write_cache_to_storage* calls under cache manager v1

## Motivation

在 cache manager v1 下，KV cache 的存储回写由 v1 内部的 RadixTree 机制处理，
resource_manager_v1 中的 write_cache_to_storage / write_cache_to_storage_decode
调用属于冗余，应跳过。

## Modifications

- resource_manager_v1.py：preemption 路径的两处存储回写调用（decode/非decode）加上
  `and not self.enable_cache_manager_v1` 条件，v1 下不再触发
- cache_manager/v1/cache_manager.py：prefix caching 未启用时，补充初始化
  `request._match_result = MatchResult()`，避免后续访问空属性

## Usage or Command

启动服务时设置 `--enable-cache-manager-v1` 即可复现修复效果：

```bash
python -m fastdeploy.entrypoints.openai.api_server \
  --enable-cache-manager-v1 \
  ...
```

Author: kevincheng2

fastdeploy/cache_manager/v1/cache_manager.py

@@ -503,6 +503,7 @@ def match_prefix(
             None. Match result is stored in request._match_result.
         """
         if not self.enable_prefix_caching or self._radix_tree is None:
+            request._match_result = MatchResult()
             return
 
         with self._lock:

fastdeploy/engine/sched/resource_manager_v1.py

@@ -482,13 +482,13 @@ def _trigger_preempt(self, request, num_new_blocks, preempted_reqs, batch_reques
                         del self.requests[preempted_req.request_id]
                     if preempted_req.request_id in self.req_dict:
                         del self.req_dict[preempted_req.request_id]
-                    if envs.FD_SAVE_OUTPUT_CACHE_FOR_PREEMPTED_REQUEST:
+                    if envs.FD_SAVE_OUTPUT_CACHE_FOR_PREEMPTED_REQUEST and not self.enable_cache_manager_v1:
                         if self.config.cache_config.kvcache_storage_backend:
                             self.cache_manager.write_cache_to_storage_decode(preempted_req)
                     self._free_blocks(preempted_req)
                     llm_logger.info(f"Preemption is triggered! Preempted request id: {preempted_req.request_id}")
                 else:
-                    if envs.FD_SAVE_OUTPUT_CACHE_FOR_PREEMPTED_REQUEST:
+                    if envs.FD_SAVE_OUTPUT_CACHE_FOR_PREEMPTED_REQUEST and not self.enable_cache_manager_v1:
                         if self.config.cache_config.kvcache_storage_backend:
                             self.cache_manager.write_cache_to_storage(preempted_req)
                     self._free_blocks(preempted_req)