[data.augmentations] Re-enable within-batch parallelisation of elastic deformation

src/ptbench/data/augmentations.py

@@ -257,7 +257,7 @@ class ElasticDeformation:
         spline_order: int = 1,
         mode: str = "nearest",
         p: float = 1.0,
-        parallel: int = -1,
+        parallel: int = -2,
     ):
         self.alpha: float = alpha
         self.sigma: float = sigma