🔧 Add forward children iterator for flex layout

Avoid Vec allocation + reverse for reversed flex layouts.
The new children_ids_iter_forward returns children in original order,
eliminating the need to collect and reverse.

render-wasm/src/shapes.rs

@@ -1119,6 +1119,25 @@ impl Shape {
         }
     }
 
+    /// Returns children in forward (non-reversed) order - useful for layout calculations
+    pub fn children_ids_iter_forward(&self, include_hidden: bool) -> Box<dyn Iterator<Item = &Uuid> + '_> {
+        if include_hidden {
+            return Box::new(self.children.iter());
+        }
+
+        if let Type::Bool(_) = self.shape_type {
+            Box::new([].iter())
+        } else if let Type::Group(group) = self.shape_type {
+            if group.masked {
+                Box::new(self.children.iter().skip(1))
+            } else {
+                Box::new(self.children.iter())
+            }
+        } else {
+            Box::new(self.children.iter())
+        }
+    }
+
     pub fn all_children(
         &self,
         shapes: ShapesPoolRef,

render-wasm/src/shapes/modifiers/flex_layout.rs

@@ -184,15 +184,18 @@ fn initialize_tracks(
 ) -> Vec<TrackData> {
     let mut tracks = Vec::<TrackData>::new();
     let mut current_track = TrackData::default();
-    let mut children = shape.children_ids(true);
     let mut first = true;
 
-    if flex_data.is_reverse() {
-        children.reverse();
-    }
+    // When is_reverse() is true, we need forward order (children_ids_iter_forward).
+    // When is_reverse() is false, we need reversed order (children_ids_iter).
+    let children_iter: Box<dyn Iterator<Item = Uuid>> = if flex_data.is_reverse() {
+        Box::new(shape.children_ids_iter_forward(true).copied())
+    } else {
+        Box::new(shape.children_ids_iter(true).copied())
+    };
 
-    for child_id in children.iter() {
-        let Some(child) = shapes.get(child_id) else {
+    for child_id in children_iter {
+        let Some(child) = shapes.get(&child_id) else {
             continue;
         };