feat: hnsw embedding server and csr format

packages/leann-core/src/leann/registry.py

@@ -1,10 +1,13 @@
 # packages/leann-core/src/leann/registry.py
 
-# 全局的后端注册表字典
-BACKEND_REGISTRY = {}
+from typing import Dict, TYPE_CHECKING
+if TYPE_CHECKING:
+    from leann.interface import LeannBackendFactoryInterface
+
+BACKEND_REGISTRY: Dict[str, 'LeannBackendFactoryInterface'] = {}
 
 def register_backend(name: str):
-    """一个用于注册新后端类的装饰器。"""
+    """A decorator to register a new backend class."""
     def decorator(cls):
         print(f"INFO: Registering backend '{name}'")
         BACKEND_REGISTRY[name] = cls