chore: New performant fade in for images

lib/widgets/mxc_image.dart

@@ -156,10 +156,17 @@ class _MxcImageState extends State<MxcImage> {
   @override
   Widget build(BuildContext context) {
     final data = _imageData;
-
-    return data == null || data.isEmpty
-        ? placeholder(context)
-        : Image.memory(
+    final hasData = data != null && data.isNotEmpty;
+
+    return Stack(
+      children: [
+        if (!hasData) placeholder(context),
+        AnimatedOpacity(
+          opacity: hasData ? 1 : 0,
+          duration: FluffyThemes.animationDuration,
+          curve: FluffyThemes.animationCurve,
+          child: hasData
+              ? Image.memory(
                   data,
                   width: widget.width,
                   height: widget.height,
@@ -171,6 +178,13 @@ class _MxcImageState extends State<MxcImage> {
                     WidgetsBinding.instance.addPostFrameCallback(_tryLoad);
                     return placeholder(context);
                   },
+                )
+              : SizedBox(
+                  width: widget.width,
+                  height: widget.height,
+                ),
+        ),
+      ],
     );
   }
 }