Better fix for exposure drift with more complete testing. Also fix return value for capture_to_memory

src/openflexure_microscope_server/things/camera/__init__.py

@@ -342,7 +342,7 @@ class BaseCamera(lt.Thing):
         logger: lt.deps.InvocationLogger,
         metadata_getter: lt.deps.GetThingStates,
         buffer_max: int = 1,
-    ) -> None:
+    ) -> int:
         """Capture an image to memory. This can be saved later with ``save_from_memory``.
 
         Note that only one image is held in memory so this will overwrite any image