Auto merge of #17672 - sadmansk:heap_in_box, r=jdm

Use boxed slice instead of vec for FuntionTimerCallback

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Added `fn trace()` implementation for `Box<[T]>` type, and change FunctionTimerCallback to store boxed slices for heap values instead of Vector.

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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #17611

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- [x] These changes do not require tests

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components/script/dom/bindings/trace.rs

@@ -177,6 +177,14 @@ unsafe impl<T: JSTraceable + ?Sized> JSTraceable for Box<T> {
     }
 }
 
+unsafe impl<T: JSTraceable> JSTraceable for [T] {
+    unsafe fn trace(&self, trc: *mut JSTracer) {
+        for e in self.iter() {
+            e.trace(trc);
+        }
+    }
+}
+
 unsafe impl<T: JSTraceable + Copy> JSTraceable for Cell<T> {
     unsafe fn trace(&self, trc: *mut JSTracer) {
         self.get().trace(trc)