Jobs with large state take a long time to show in UI

If a job has a very large array (a few MBs) of some internal state, that whole value is downloaded to the browser in the UI. I think that some values, e.g. ones that begin with '_', should not be downloaded, allowing much more efficient job management.

No file or test is named in the issue. Start by tracing how job state is fetched for the UI and where values are serialized for the browser; done means large internal values such as underscore-prefixed state are not downloaded while the job remains manageable in the UI.

Written by the indexing model from the issue text.