Tree widget: Telemetry enhancements

[grigasp]

1. Need some way to know about errors happening in the widget. Maybe we could report them as "features", e.g. error-timeout, error-unknown?..

2. From performance telemetry numbers it's not clear if the value is for a successful result or an error result. For the latter, I even think we should distinguish timeouts and other kinds of errors:

   • for successful results, return the duration as we do at the moment,
   • for timeout results, return a constant large number, maybe MAX_INTEGER,
   • for non-timeout error results, don't report performance telemetry.