Minor fixes for tests (#4686)

* Suggested method for correcting integration tests

* Use static atomics for simplicity

This is consistent with the test immediately below.

* Add assertions to some tests, comments to others

This should fix a handful of tests that didn't correctly do their test.

In other places, comments should make it clearer *why* tests are how
they are.

* Be consistent with existing imports

* remove bad test

* nit

* fix compile errrs

---------

Co-authored-by: Jonathan Kelley <jkelleyrtp@gmail.com>

packages/core/tests/miri_full_app.rs

@@ -3,6 +3,8 @@ use dioxus_core::ElementId;
 use dioxus_elements::SerializedHtmlEventConverter;
 use std::{any::Any, rc::Rc};
 
+// This test is intended to be run with Miri, and contains no assertions. If it completes under
+// Miri, it has passed.
 #[test]
 fn miri_rollover() {
     set_event_converter(Box::new(SerializedHtmlEventConverter));