Change Zed2i serial_number type hint to Optional[int]

The ZED API expects an integer serial number, not a string

airo-camera-toolkit/airo_camera_toolkit/cameras/zed/zed2i.py

@@ -84,7 +84,7 @@ def __init__(  # type: ignore[no-any-unimported]
         resolution: CameraResolutionType = RESOLUTION_2K,
         fps: int = 15,
         depth_mode: sl.DEPTH_MODE = NONE_DEPTH_MODE,
-        serial_number: Optional[str] = None,
+        serial_number: Optional[int] = None,
         svo_filepath: Optional[str] = None,
     ) -> None:
         self._resolution = resolution