Ship the NIEL damage weights as CSV

This adds the RD50 damage weights in the text format the Geant4 fluence weighting reads.

- G4.fluenceWeightFile accepts CSV only, while Detectors/gconfig/data so far held the weights as ROOT graphs.
- The file is dumped from rd50_niel.root and carries the same values.
- The existing o2_data_file rule installs it to share/Detectors/gconfig/data/.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: sawenzel