Add SafeTensors consolidation stage for zero-copy tensor loading

Bundle all per-image modalities (depth, edge, chm, segm) into a single
.safetensors file for fast training DataLoader reads (~0.1ms zero-copy mmap
vs ~5ms for 4x PNG). Adds consolidate stage after main pipeline stages,
save_safetensors/cleanup_npy config flags, resume support, and 10 new tests.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

in/config_files/pipeline.gin

@@ -5,6 +5,8 @@ PipelineConfig.stages = ['depth', 'edges', 'segmentation', 'chmv2']
 PipelineConfig.save_npy = False
 PipelineConfig.save_vis = True
 PipelineConfig.save_concat = False
+PipelineConfig.save_safetensors = True
+PipelineConfig.cleanup_npy = False
 PipelineConfig.resume = True
 PipelineConfig.subset = None
 # Source filter: 'db' = satellite only, 'query' = drone/UAV only, None = both