add StartedTestRun type state

- this new type disallows users to misuse the run (eg. by emitting run
  artifacts when the run hasn't been started yet)
- this also shows that there is little value in having a TestRun object
  around, while not having started, due to the only action possible on
  it is to start it. It may be beneficial in the future to only allow
  started objects to exist, instead of having inert objects passed
  around. This is a slight change in usage, but not very consequential.
- also fix macros tests since this new StartedTestRun pattern
  highlighted that they were emitting invalid messages

Signed-off-by: mimir-d <[email protected]>