NetworkHelper Singleton isn't thread safe #3197
Description
Describe the bug
Noticed while working on unit tests that NetworkHelper isn't thread safe as we're assigning to a field instead of just using the property backing. We should update to the same pattern we used in #3168. I think in this case though, it's debatable whether it'd be a breaking change, probably best to put in 7.0 to be safe.
We should probably do an Audit in general of any Singleton patterns within the Toolkit, it seems like there may be other cases? See #3134 for more details.