test: Add an automatic timeout to some of the tests functions [EE-462]

Something is hanging occasionally in the fuzz tests. It almost definitely isn't just a test ending up taking a long time, because the default test timeout in the fuzz tests in the pipelines is 4 minutes!

This MR adds timeouts to the likely suspects (messaging the background page and messaging the webdriver runner), and will hopefully make it error with a better error message next time. That will help us to figure out where is actually hanging.