Always import pi from backend

Author: FlorianPfaff

pyrecest/tests/distributions/test_hyperspherical_grid_distribution.py

@@ -1,14 +1,14 @@
 import copy
 import unittest
 import warnings
-from math import pi
 
 import numpy.testing as npt
 import pyrecest
 from pyrecest.backend import (
     allclose,
     array,
     cos,
+    pi,
     eye,
     linspace,
     meshgrid,