fix caching when using combined loader

Author: ziw-liu

viscy/data/combined.py

@@ -40,9 +40,11 @@ def __init__(
         self.val_mode = CombineMode(val_mode).value
         self.test_mode = CombineMode(test_mode).value
         self.predict_mode = CombineMode(predict_mode).value
+        self.prepare_data_per_node = True
 
     def prepare_data(self):
         for dm in self.data_modules:
+            dm.trainer = self.trainer
             dm.prepare_data()
 
     def setup(self, stage: Literal["fit", "validate", "test", "predict"]):