feat: add missing methods for the Operations to the interface file

taskchampion.pyi

@@ -59,7 +59,11 @@ class Operation:
     value: Optional[str]
 
 class Operations:
-    def append(op: "Operation"): ...
+    def append(self, op: "Operation"): ...
+    def __len__(self) -> int: ...
+    def __iter__(self) -> Iterator["Operation"]: ...
+    def __next__(self) -> "Operation": ...
+    def __getitem__(self, i: int) -> "Operation": ...
 
 class Status(Enum):
     Pending = 1