[HiCache] Clear kvcache in storage backend with fastAPI (#9750)

Co-authored-by: hzh0425 <hzh0425@apache.org>

python/sglang/srt/managers/io_struct.py

@@ -814,6 +814,16 @@ class BatchEmbeddingOut:
     cached_tokens: List[int]
 
 
+@dataclass
+class ClearHiCacheReqInput:
+    pass
+
+
+@dataclass
+class ClearHiCacheReqOutput:
+    success: bool
+
+
 @dataclass
 class FlushCacheReqInput:
     pass