Fix: Replace CDC integer index lookup with image_key strings

Fixes shape mismatch bug in multi-subset training where CDC preprocessing
and training used different index calculations, causing wrong CDC data to
be loaded for samples.

Changes:
- CDC cache now stores/loads data using image_key strings instead of integer indices
- Training passes image_key list instead of computed integer indices
- All CDC lookups use stable image_key identifiers
- Improved device compatibility check (handles "cuda" vs "cuda:0")
- Updated all 30 CDC tests to use image_key-based access

Root cause: Preprocessing used cumulative dataset indices while training
used sorted keys, resulting in mismatched lookups during shuffled multi-subset
training.

library/train_util.py

@@ -1569,18 +1569,14 @@ class BaseDataset(torch.utils.data.Dataset):
         flippeds = []  # 変数名が微妙
         text_encoder_outputs_list = []
         custom_attributes = []
-        indices = []  # CDC-FM: track global dataset indices
+        image_keys = []  # CDC-FM: track image keys for CDC lookup
 
         for image_key in bucket[image_index : image_index + bucket_batch_size]:
             image_info = self.image_data[image_key]
             subset = self.image_to_subset[image_key]
 
-            # CDC-FM: Get global index for this image
-            # Create a sorted list of keys to ensure deterministic indexing
-            if not hasattr(self, '_image_key_to_index'):
-                self._image_key_to_index = {key: idx for idx, key in enumerate(sorted(self.image_data.keys()))}
-            global_idx = self._image_key_to_index[image_key]
-            indices.append(global_idx)
+            # CDC-FM: Store image_key for CDC lookup
+            image_keys.append(image_key)
 
             custom_attributes.append(subset.custom_attributes)
 
@@ -1827,8 +1823,8 @@ class BaseDataset(torch.utils.data.Dataset):
 
         example["network_multipliers"] = torch.FloatTensor([self.network_multiplier] * len(captions))
 
-        # CDC-FM: Add global indices to batch
-        example["indices"] = torch.LongTensor(indices)
+        # CDC-FM: Add image keys to batch for CDC lookup
+        example["image_keys"] = image_keys
 
         if self.debug_dataset:
             example["image_keys"] = bucket[image_index : image_index + self.batch_size]