Add experimental half precison support

With this MR experimental half-precision support is added

pystencils/cpu/cpujit.py

@@ -43,20 +43,21 @@ Then 'cl.exe' is used to compile.
   For Windows compilers the qualifier should be ``__restrict``
 
 """
+from appdirs import user_cache_dir, user_config_dir
+from collections import OrderedDict
 import hashlib
 import json
 import os
 import platform
 import shutil
 import subprocess
-import textwrap
-import warnings
-from collections import OrderedDict
 from sysconfig import get_paths
 from tempfile import TemporaryDirectory, NamedTemporaryFile
+import textwrap
+import time
+import warnings
 
 import numpy as np
-from appdirs import user_cache_dir, user_config_dir
 
 from pystencils import FieldType
 from pystencils.astnodes import LoopOverCoordinate
@@ -477,8 +478,6 @@ def load_kernel_from_file(module_name, function_name, path):
         mod = module_from_spec(spec)
         spec.loader.exec_module(mod)
     except ImportError:
-        import time
-        import warnings
         warnings.warn(f"Could not load {path}, trying on more time in 5 seconds ...")
         time.sleep(5)
         spec = spec_from_file_location(name=module_name, location=path)