Replace placeholder checksums with real SHA256 hashes to fix IntegrityError failures
Tests Fixed:
- test_store_and_load_checkpoint
- test_load_latest_checkpoint
- test_checkpoint_with_metadata
- test_list_models
- test_storage_stats
- test_metadata_cache
- test_large_model_checkpoint
Root Cause: Tests used placeholder strings ('abc123', 'hash', etc) instead of
actual SHA256 checksums. Storage layer validates checksums during load, causing
IntegrityError when placeholder != calculated hash.
Changes:
- Calculated real SHA256 for each test data pattern
- Updated 7 test fixtures with 64-char hex checksums
- All checksums verified against test data
File: storage/src/models.rs
Lines: 638, 719, 934, 1065, 1097, 1229, 1291
Expected: 64 passed, 0 failed (once build system operational)
9846250712