[data.datamodule] Adjust sample storage size calculation

src/ptbench/data/datamodule.py

@@ -49,7 +49,8 @@ def _sample_size_bytes(s: Sample) -> int:
         """Returns a tensor size in bytes."""
         return int(t.element_size() * torch.prod(torch.tensor(t.shape)))
 
-    size = int(s[0].element_size() * torch.prod(torch.tensor(s[0].shape)))
+    size = sys.getsizeof(s[0])  # tensor metadata
+    size += int(s[0].element_size() * torch.prod(torch.tensor(s[0].shape)))
     size += sys.getsizeof(s[1])
 
     # check each element - if it is a tensor, then adds its total space in