Speed up per-frame layout, hit testing, and stacking paths

Split ScrollingLayout validation so the per-frame geometry solve only
checks scalars and keeps the full tree validation behind debug_assert,
removing a HashSet build from every frame. Replace the per-region Vec
in decode_regions with a stack array via as_chunks, and skip the window
hit test in PointerMotion when Overview is not presenting, where
visual_scale_for_window returns 1.0 regardless.

Guard sync_window_stacking behind a check that the space already matches
the target order with uniform z_index, avoiding an O(n^2) raise_element
loop on every redraw. Narrow window_under_visual to the space iterator
outside Overview, keeping the collected and sorted candidate list for
the Overview branch where front-to-back order is load-bearing.

Raise rust-version to 1.98 and clear the resulting Clippy findings
across the workspace: let-chain collapses, clamp, and while-let loops.

crates/ferese-config/src/lib.rs

@@ -39,6 +39,7 @@ pub fn default_wallpaper() -> &'static str {
             .unwrap_or_else(|| {
                 PathBuf::from(env!("CARGO_MANIFEST_DIR")).join("../../assets/wallpapers/ferese.png")
             });
+
         path.canonicalize()
             .unwrap_or(path)
             .to_string_lossy()
@@ -50,6 +51,7 @@ fn field(name: &str, parent: &str) -> String {
     if parent == "commands" {
         return name.to_owned();
     }
+
     match name {
         "binding" => "bindings".into(),
         "window-rule" => "window_rules".into(),
@@ -61,11 +63,14 @@ fn field(name: &str, parent: &str) -> String {
 }
 
 fn is_records(key: &str, parent: &str) -> bool {
-    match (parent, key) {
-        ("", "bindings" | "window_rules" | "output_profiles" | "autostart") => true,
-        ("output_profiles", "outputs") | ("desktop_widgets", "notes") => true,
-        _ => false,
-    }
+    matches!(
+        (parent, key),
+        (
+            "",
+            "bindings" | "window_rules" | "output_profiles" | "autostart"
+        ) | ("output_profiles", "outputs")
+            | ("desktop_widgets", "notes")
+    )
 }
 
 fn is_array(key: &str, parent: &str) -> bool {
@@ -365,11 +370,11 @@ fn restore_node_formats(doc: &mut KdlDocument, formats: &mut impl Iterator<Item
                     entry.set_format(format);
                 }
             }
-            if let Some(terminator) = terminator {
-                if let Some(format) = node.format_mut() {
-                    format.before_terminator = " ".into();
-                    format.terminator = terminator;
-                }
+            if let Some(terminator) = terminator
+                && let Some(format) = node.format_mut()
+            {
+                format.before_terminator = " ".into();
+                format.terminator = terminator;
             }
         }
         if let Some(children) = node.children_mut() {
@@ -519,15 +524,14 @@ fn set_in(doc: &mut KdlDocument, parts: &[&str], parent: &str, value: Value) ->
     }
     let node = &mut doc.nodes_mut()[i];
 
-    if parts.len() == 2 {
-        if let Some(entry) = node
+    if parts.len() == 2
+        && let Some(entry) = node
             .entries_mut()
             .iter_mut()
             .find(|e| e.name().is_some_and(|n| field(n.value(), key) == parts[1]))
-        {
-            set_entry_value(entry, kdl_value(&value)?);
-            return Ok(());
-        }
+    {
+        set_entry_value(entry, kdl_value(&value)?);
+        return Ok(());
     }
 
     set_in(

crates/ferese-layout/src/scrolling.rs

@@ -456,7 +456,10 @@ impl ScrollingLayout {
         if let Some(focused) = focused {
             self.focus(focused)?;
         }
-        self.validate()?;
+
+        self.validate_scalars()?;
+        debug_assert!(self.validate().is_ok());
+
         if self.columns.is_empty() {
             self.viewport_x = 0.0;
             return Ok(LayoutResult::default());
@@ -673,7 +676,7 @@ impl ScrollingLayout {
         })
     }
 
-    pub fn validate(&self) -> Result<(), LayoutError> {
+    fn validate_scalars(&self) -> Result<(), LayoutError> {
         if !self.viewport_x.is_finite() {
             return Err(LayoutError::InvalidTree(
                 "scrolling viewport offset is invalid",
@@ -701,6 +704,11 @@ impl ScrollingLayout {
                 "scrolling active column is invalid",
             ));
         }
+        Ok(())
+    }
+
+    pub fn validate(&self) -> Result<(), LayoutError> {
+        self.validate_scalars()?;
 
         let mut windows = HashSet::new();
         for column in &self.columns {