* Set the async local just before execution.
- Subscribing to DiagnosticListener.AllListeners replays all created DiagnosticListener instances. Because of this, we need to set the async local just before the execution of the entry point so that we only collect the events that are relevant to the call. Right now, it's also firing with the async local set pre-maturely.
- Wrote a concurrency test to make sure it's safe to instantiate the factory in parallel.