OnShow and OnHide fire children first, and after OnLoad, as in 1.12.1 (#842)

Show and hide propagated a whole subtree first, then fired from a snapshot, parent first: a parent's `OnShow` ran before its children's, and a child hidden by an earlier handler still got its `OnShow`. A frame visible at the end of its load got no `OnShow` at all.

In 1.12.1 show `0x76ae10` and hide `0x76ad50` mark the frame, walk the live child list re-checking each child's gate, and fire the frame's own handler last (`0x76aef5`, `0x76adfd`). The post-load hook fires `OnShow` after `OnLoad` for a visible frame (`0x76a3b3`), from XML and `CreateFrame` alike.

Now handlers run inside a live post-order walk, and the post-load `OnShow` fires. Tests cover the order, a sibling hidden mid-walk, and one or two `OnShow`s after a load; they fail without the fix. Four existing tests' expected orders flip to the reference's.

Fixes #350
Fixes #59

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Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/benilla-ui/src/script/tooltip/mod.rs

@@ -355,13 +355,9 @@ fn now(lua: &Lua) -> f64 {
     crate::script::clock::now(lua)
 }
 
-/// Shows or hides through the arena and fires the visibility events.
+/// Shows or hides as the Lua verbs do, handlers included.
 pub(super) fn set_shown(lua: &Lua, h: FrameHandle, shown: bool) {
-    let changed = {
-        let mut model = lua.app_data_mut::<Model>().expect("model app_data");
-        model.arena.set_shown(h, shown)
-    };
-    event::fire_visibility_changes(lua, changed);
+    crate::script::visibility::set_shown(lua, h, shown);
 }
 
 /// The default line colour, gold `0xffffd200` (stored at `0xc0d3e8` by `0x528e50`). The zone