Validation framework

[janvis11]

Module: validation_framework.py

Description: Comprehensive validation framework for coastline extraction
accuracy assessment and improvement quantification.

         Features:
         - Transect-based RMSE calculation
         - IoU/Dice metrics for segmentation
         - Per-region accuracy analysis (cliff vs. non-cliff)
         - Comparison against ground truth
         - Statistical significance testing
         - Visualization of results