This moves the navigation span starting into its own method since it
will likely be needed elsewhere.

It looks like we weren't ending the span when a new navigation span was
being started.

The navigation span was started a lot later than it should have. This
meant that child spans (such as web vitals) looked incorrect since
the values of those child spans were longer than the navigation span.

Now the navigation span is started a lot earlier, and this means that
the child span values are safely within the permitted navigation span.

We still have a navigation span start from onFrameNavigated which is
needed when the iteration starts on a new page, since
onFrameStartedLoading isn't called when a new page is called and it
navigates to about:blank.

When the navigation span is started, the new URL is not available to us
yet. We have to defer the adding of the url attribute to the span to
the end of the navigation span.

It was useful to have a test to ensure that the navigation spans were
created in the expected order before and after the fix.

This is to help mimic expected test structure. The page.close should
help determine when the test ends and whether there are any anomalies.

This also protects the retrieval of the url with the mutex.

Adding better ways of waiting for API to end with the use of waitUntil
and waitForNavigation. Now comparing the elements within the slices
and not worrying about the order since the order can change on every
test run.

- Rename it to better represent what it is doing and the cost of the
action.
- Use clone instead of copy.

This isn't available in go <1.21 so reverting to copy for now.