fix(mobile): race condition showing details (#26559)

Asset details are prematurely hidden when a drag ends if the simulation
shows that it will close given its current velocity. It makes for a much
more responsible feeling UI. However, this behaviour conflicts with the
logic which determines whether details are showing based on the current
offset. The result is that the details are hidden, then immediately
shown again, and then hidden once it passes the min snap distance
threshold.

This can be fixed by only evaluating the position based logic when a
drag is active, and then inferring upcoming state with a simulation.

mobile/lib/presentation/widgets/asset_viewer/asset_page.widget.dart

@@ -64,7 +64,6 @@ class _AssetPageState extends ConsumerState<AssetPage> {
   @override
   void initState() {
     super.initState();
-    _proxyScrollController.addListener(_onScroll);
     _eventSubscription = EventStream.shared.listen(_onEvent);
     WidgetsBinding.instance.addPostFrameCallback((_) {
       if (!mounted || !_proxyScrollController.hasClients) return;
@@ -94,6 +93,7 @@ class _AssetPageState extends ConsumerState<AssetPage> {
 
   void _showDetails() {
     if (!_proxyScrollController.hasClients || _snapOffset <= 0) return;
+    _viewer.setShowingDetails(true);
     _proxyScrollController.animateTo(_snapOffset, duration: Durations.medium2, curve: Curves.easeOutCubic);
   }
 
@@ -105,7 +105,7 @@ class _AssetPageState extends ConsumerState<AssetPage> {
         SnapScrollPhysics.target(position, scrollVelocity, _snapOffset) < SnapScrollPhysics.minSnapDistance;
   }
 
-  void _onScroll() {
+  void _syncShowingDetails() {
     final offset = _proxyScrollController.offset;
     if (offset > SnapScrollPhysics.minSnapDistance) {
       _viewer.setShowingDetails(true);
@@ -149,6 +149,8 @@ class _AssetPageState extends ConsumerState<AssetPage> {
       case _DragIntent.scroll:
         if (_drag == null) _startProxyDrag();
         _drag?.update(details);
+
+        _syncShowingDetails();
       case _DragIntent.dismiss:
         _handleDragDown(context, details.localPosition - _dragStart!.localPosition);
     }
@@ -167,9 +169,8 @@ class _AssetPageState extends ConsumerState<AssetPage> {
       case _DragIntent.none:
       case _DragIntent.scroll:
         final scrollVelocity = -(details.primaryVelocity ?? 0.0);
-        if (_willClose(scrollVelocity)) {
-          _viewer.setShowingDetails(false);
-        }
+        _viewer.setShowingDetails(!_willClose(scrollVelocity));
+
         _drag?.end(details);
         _drag = null;
       case _DragIntent.dismiss: