Introduce a `debug_mode` flag to the `Environment` and a new `run_debug`
method. This method uses a `TracingObserver` to log the VM's execution
flow, including node evaluation and scope state changes. This allows for
detailed inspection of script execution.
The `BoundKind` enum now also includes a `display_name` method for
better log readability.
Michael Schimmel
faada16723