Fix: Add missing typehints

Author: domstoppable

src/pupil_labs/realtime_api/streaming/gaze.py

@@ -475,11 +475,11 @@ def from_raw(cls, data: RTSPData) -> "EyestateEyelidDualMonoGazeData":
         )
 
     @property
-    def datetime(self):
+    def datetime(self) -> datetime.datetime:
         return datetime.datetime.fromtimestamp(self.timestamp_unix_seconds)
 
     @property
-    def timestamp_unix_ns(self):
+    def timestamp_unix_ns(self) -> int:
         return int(self.timestamp_unix_seconds * 1e9)