fixup! refactor(timeline): Make RoomDataProvider provide Decryptor to simplify redecryption

Improve comment

Author: andybalaam

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

@@ -160,7 +160,8 @@ pub(super) struct TimelineController<P: RoomDataProvider = Room> {
 
     /// A [`RoomDataProvider`] implementation, providing data.
     ///
-    /// In the real world, this is just a [`Room`].
+    /// The type is a `RoomDataProvider` to allow testing. In the real world,
+    /// this would normally be a [`Room`].
     pub(crate) room_data_provider: P,
 
     /// Settings applied to this timeline.