Added missing return types to .pyi file

python/outlines_core/fsm/outlines_core_rs.pyi

@@ -88,22 +88,22 @@ class Vocabulary:
         ...
 
 class Index:
-    def get_allowed_tokens(self, state: int):
+    def get_allowed_tokens(self, state: int) -> List[int]:
         """
         Return the next instruction for guided generation.
         """
         ...
-    def get_next_state(self, state: int, token_id: int):
+    def get_next_state(self, state: int, token_id: int) -> Optional[int]:
         """
         Update the state of the guide.
         """
         ...
-    def is_final_state(self, state: int):
+    def is_final_state(self, state: int) -> bool:
         """Determine whether the current state of the guide is a final state."""
         ...
-    def get_index_dict(self):
+    def get_index_dict(self) -> Dict[int, Dict[int, int]]:
         """Returns the Index as a Python Dict object."""
         ...
-    def get_initial_state(self):
+    def get_initial_state(self) -> int:
         """Returns the ID of the initial state of the input FSM automata."""
         ...