add typing for secure aggregation

Signed-off-by: weiwee <wbwmat@gmail.com>

rust/fate_utils/python/fate_utils/secure_aggregation_helper/__init__.pyi

@@ -0,0 +1,18 @@
+from typing import List, Dict, Optional, Tuple
+import numpy as np
+
+class DiffieHellman:
+    def __init__(self) -> None: ...
+    def get_public_key(self) -> bytes: ...
+    def diffie_hellman(self, other_public_key: bytes) -> bytes: ...
+
+class RandomMix:
+    def __init__(self, seeds: Dict[int, bytes], rank: int) -> None: ...
+    def mix_one(self, input: np.ndarray, weight: Optional[float] = None) -> Tuple[np.ndarray, np.ndarray]: ...
+    def mix(self, inputs: List[np.ndarray], weight: Optional[float] = None) -> List[Tuple[np.ndarray, np.ndarray]]: ...
+    def get_index(self, rank: int) -> int: ...
+
+class MixAggregate:
+    def __init__(self) -> None: ...
+    def aggregate(self, inputs: List[Tuple[np.ndarray, np.ndarray]]) -> None: ...
+    def finalize(self, weight: Optional[float] = None) -> List[np.ndarray]: ...