task(ui): TimelineState::handle_remote_events_with_diffs adjusts the Skip's count.

This patch updates `TimelineState::handle_remote_events_with_diffs` to
adjust the count value of the `Skip` higher-order stream.

Author: Hywan

crates/matrix-sdk-ui/src/timeline/controller/state.rs

@@ -97,9 +97,23 @@ impl TimelineState {
             return;
         }
 
+        let previous_number_of_items = self.items.len();
+
         let mut transaction = self.transaction();
         transaction.handle_remote_events_with_diffs(diffs, origin, room_data, settings).await;
         transaction.commit();
+
+        let next_number_of_items = self.items.len();
+
+        // Calculate the new count value for the `Skip` stream, used by the `Timeline`
+        // subscriber.
+        let count = self
+            .meta
+            .subscriber_skip_count
+            .compute_next(previous_number_of_items, next_number_of_items);
+
+        // Update the count value for the `Skip` stream.
+        self.meta.subscriber_skip_count.update(count, &self.timeline_focus);
     }
 
     /// Marks the given event as fully read, using the read marker received from