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_simple.rs

@@ -1,6 +1,9 @@
 use dioxus::prelude::*;
 use dioxus_core::generation;
 
+// The tests in this file are intended to be run with Miri, and contain no assertions. If they
+// complete under Miri, they have passed.
+
 #[test]
 fn app_drops() {
     fn app() -> Element {