Implements core seasonal baseline functionality for EO anomaly detection:
- group_bands_by_calendar_month: Maps multi-year band indices to calendar months
- compute_seasonal_stats_aoi: Computes per-month AOI-level stats from baseline raster
- compute_seasonal_stats_pixel: Computes per-pixel statistics across bands
- compute_zscore: Computes z-scores with std-floor to avoid division-by-zero
All 6 tests pass.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
