Fix: Use round instead of int for duration updates

Create and other places already use round(), so this
makes it more consistent.

Signed-off-by: Mathias L. Baumann <[email protected]>

Author: Marenz

src/frequenz/client/dispatch/_client.py

@@ -325,7 +325,7 @@ async def update(
                 case "start_time":
                     msg.update.start_time.CopyFrom(to_timestamp(val))
                 case "duration":
-                    msg.update.duration = int(val.total_seconds())
+                    msg.update.duration = round(val.total_seconds())
                 case "selector":
                     msg.update.selector.CopyFrom(component_selector_to_protobuf(val))
                 case "is_active":