Add plasma bubble QD-to-geodetic conversion

[Nova-David]

• Adds convert_qd.py: converts a real 4-year (Oct 2018–Sep 2022) equatorial plasma bubble detection dataset from NASA's GOLD mission into geographic coordinates comparable to the project's existing satellite/ground-station data.
• Merges three region CSVs (north, equatorial, south), tagging each row with its source region before concatenating, since each region file uses a different convention for its QD Latitude column (equatorial is fixed at 0; north/south record the EIA crest, not the bubble itself).
• Converts QD (Quasi-Dipole) coordinates to geographic lat/lon via apexpy, building a separate magnetic field model per year (apexpy.Apex(date=year)) rather than one fixed transform, since Earth's magnetic field drifts year to year. Conversion uses a fixed 300km reference height, matching where the underlying airglow signature originates.
• Computes each bubble's radius as half the great-circle distance between its west and east edges (both converted through the same year-aware transform), rather than inventing a QD-degree-to-km scale factor. Matches the dataset's own methods paper (bubble-separation calculations, Sec 4.6).
• Preserves each detection's track ID (unique within its region, not globally) so a single bubble can be followed across successive scans as it drifts.
• Outputs one .npz with 81,164 detections, each carrying region, track ID, UTC timestamp, both QD and converted geographic coordinates, radius in km, and the underlying detection-algorithm outputs (EIA radiance, Gaussian fit coefficient).
• Coordinate conversion only.