MatrixRoom API refinement (#719)

- `syncUpdateFlow` becomes a `val` and always returns the same instance of the underlying `StateFlow` instead of different `Flow` instances to allow consumers not to remember the `Flow` and not to specify an unneeded initial value.
- `timeline` becomes a `val` as it already always returns the same instance.
- Amends calling code accordingly
- Removes a few unneeded `val`s in `RustMatrixClient
- Fixes a small bug in `MessagesPresenter` that allowed to sometime show a newly created room's name as "Empty room" (changes `LaunchedEffect(syncUpdateFlow)` to `LaunchedEffect(syncUpdateFlow.value)`)

features/messages/impl/src/main/kotlin/io/element/android/features/messages/impl/MessagesPresenter.kt

@@ -99,7 +99,7 @@ class MessagesPresenter @AssistedInject constructor(
         val customReactionState = customReactionPresenter.present()
         val retryState = retrySendMenuPresenter.present()
 
-        val syncUpdateFlow = room.syncUpdateFlow().collectAsState(0L)
+        val syncUpdateFlow = room.syncUpdateFlow.collectAsState()
         val userHasPermissionToSendMessage by room.canSendEventAsState(type = MessageEventType.ROOM_MESSAGE, updateKey = syncUpdateFlow.value)
         val roomName: MutableState<String?> = rememberSaveable {
             mutableStateOf(null)
@@ -112,7 +112,7 @@ class MessagesPresenter @AssistedInject constructor(
 
         val snackbarMessage by snackbarDispatcher.collectSnackbarMessageAsState()
 
-        LaunchedEffect(syncUpdateFlow) {
+        LaunchedEffect(syncUpdateFlow.value) {
             roomAvatar.value =
                 AvatarData(
                     id = room.roomId.value,

features/messages/impl/src/main/kotlin/io/element/android/features/messages/impl/timeline/TimelinePresenter.kt

@@ -43,7 +43,7 @@ class TimelinePresenter @Inject constructor(
     room: MatrixRoom,
 ) : Presenter<TimelineState> {
 
-    private val timeline = room.timeline()
+    private val timeline = room.timeline
 
     @Composable
     override fun present(): TimelineState {