Avoid loading timezone at runtime (#157)

* Avoid loading timezone at runtime

Pytz will load timezone info from files in
a lazy fashion on first access. This triggers warnings in HA due to it blocking the event loop.

Pre-load the needed timezone info at module import instead, which will run in
executor in HA.

* Update value_types.py

dsmr_parser/value_types.py

@@ -2,6 +2,10 @@
 
 import pytz
 
+# TODO : Use system timezone
+# Preload timezone to avoid loading in event loop later
+local_tz = pytz.timezone('Europe/Amsterdam')
+
 
 def timestamp(value):
     try:
@@ -20,8 +24,6 @@ def timestamp(value):
     else:
         is_dst = False
 
-    # TODO : Use system timezone
-    local_tz = pytz.timezone('Europe/Amsterdam')
     localized_datetime = local_tz.localize(naive_datetime, is_dst=is_dst)
 
     return localized_datetime.astimezone(pytz.utc)