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.

shell/ferese-polkit-agent/src/session.rs

@@ -53,6 +53,7 @@ impl Api {
             let cancel = *agent
                 .get(b"polkit_agent_session_cancel\0")
                 .map_err(|e| e.to_string())?;
+
             Ok(Self {
                 _agent: agent,
                 _polkit: polkit,
@@ -199,7 +200,10 @@ fn run_session(
         connect(
             session,
             c"request",
-            Some(std::mem::transmute(
+            Some(std::mem::transmute::<
+                unsafe extern "C" fn(Object, *const c_char, c_int, *mut c_void),
+                unsafe extern "C" fn(),
+            >(
                 request as unsafe extern "C" fn(Object, *const c_char, c_int, *mut c_void),
             )),
             signal_data,
@@ -207,7 +211,10 @@ fn run_session(
         connect(
             session,
             c"show-info",
-            Some(std::mem::transmute(
+            Some(std::mem::transmute::<
+                unsafe extern "C" fn(Object, *const c_char, *mut c_void),
+                unsafe extern "C" fn(),
+            >(
                 info as unsafe extern "C" fn(Object, *const c_char, *mut c_void),
             )),
             signal_data,
@@ -215,7 +222,10 @@ fn run_session(
         connect(
             session,
             c"show-error",
-            Some(std::mem::transmute(
+            Some(std::mem::transmute::<
+                unsafe extern "C" fn(Object, *const c_char, *mut c_void),
+                unsafe extern "C" fn(),
+            >(
                 error as unsafe extern "C" fn(Object, *const c_char, *mut c_void),
             )),
             signal_data,
@@ -223,11 +233,15 @@ fn run_session(
         connect(
             session,
             c"completed",
-            Some(std::mem::transmute(
+            Some(std::mem::transmute::<
+                unsafe extern "C" fn(Object, c_int, *mut c_void),
+                unsafe extern "C" fn(),
+            >(
                 completed as unsafe extern "C" fn(Object, c_int, *mut c_void),
             )),
             signal_data,
         );
+
         (api.initiate)(session);
     }