[HiCache] fix: check clear() method for storage backend (#10096)

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

python/sglang/srt/mem_cache/hiradix_cache.py

@@ -134,11 +134,24 @@ class HiRadixCache(RadixCache):
             height += 1
         return height
 
-    def clear_storage_backend(self):
+    def clear_storage_backend(self) -> bool:
         if self.enable_storage:
-            self.cache_controller.storage_backend.clear()
-            logger.info("Hierarchical cache storage backend cleared successfully!")
-            return True
+            try:
+                # Check if the storage backend has a clear method (for nixl backends)
+                if hasattr(self.cache_controller.storage_backend, "clear"):
+                    self.cache_controller.storage_backend.clear()
+                    logger.info(
+                        "Hierarchical cache storage backend cleared successfully!"
+                    )
+                    return True
+                else:
+                    logger.warning(
+                        f"Storage backend {type(self.cache_controller.storage_backend).__name__} does not support clear operation."
+                    )
+                    return False
+            except Exception as e:
+                logger.error(f"Failed to clear hierarchical cache storage backend: {e}")
+                return False
         else:
             logger.warning("Hierarchical cache storage backend is not enabled.")
             return False