Use float64 for extensivity test

Author: ElliottKasoar

ml_peg/calcs/physicality/extensivity/calc_extensivity.py

@@ -60,6 +60,8 @@ def test_extensivity(mlip: tuple[str, Any]) -> None:
         Name of model use and model to get calculator.
     """
     model_name, model = mlip
+    # Use double precision
+    model.default_dtype = "float64"
     calc = model.get_calculator()
 
     sym1, sym2 = "Al", "Ni"  # element of slab-1 and slab-2