Add camera-stage-mapping compliant functions to BaseStage and BaseCamera.

src/openflexure_microscope_server/things/camera/opencv.py

@@ -75,6 +75,11 @@ class OpenCVCamera(BaseCamera):
             ].tobytes()
             self.lores_mjpeg_stream.add_frame(jpeg_lores, portal)
 
+    @lt.thing_action
+    def discard_frames(self) -> None:
+        """Discard frames so that the next frame captured is fresh."""
+        self.capture_array()
+
     @lt.thing_action
     def capture_array(
         self,