Parallelising spin evolution

The purpose of this MR is to speed up the spin evolution calculation by running on multiple cpus.

tests/utils_test.py

@@ -589,15 +589,6 @@ class TestTQDM(object):
             lines = f.readlines()
             assert "PESummary" in lines[-1]
             assert "INFO" in lines[-1]
-
-        for j in tqdm(self._range, logger=logger):
-            _ = j*j
-
-        with open(LOG_FILE, "r") as f:
-            data = f.readlines()
-
-        assert all("PESummary" in i for i in data if len(i))
-        assert all("DEBUG" in i for i in data if len(i))
         
 
 def test_jensen_shannon_divergence():