DOC: Report more detail for pediatric_airway_atlas failures

Currently we report only that the computation in the `pediatric_airway_atlas` module failed, and give an error message that speculates what might have gone wrong. Instead, catch any errors or exceptions from `pediatric_airway_atlas` to give a more informative and definitive message.

Note that `pediatric_airway_atlas` is invoked via `slicer.util._executePythonModule(...)` rather than by direct Python call, so the detecting and reporting of exceptions may be somewhat non-trivial.

Start by tracing where the pediatric_airway_atlas module is invoked through slicer.util._executePythonModule(...), then inspect how its current failure message is produced. Determine how exceptions from that invocation can be detected and reported; done means failures provide an informative, definitive message rather than speculation.

Written by the indexing model from the issue text.