Using of proper TZ environment

Long time now, I have troubles with tools using tasklib due to a custom setting of TZ environment variable ("CET-1", without summertime)

While python is able to work correct with that
```python
>>> import time
>>> time.tzname
('CET', 'CET')
>>> time.strftime('%X %x %Z')
'12:22:02 10/15/21 CET'
```

The Approach of tzlocal using ZoneInfo is completely broken and gives exceptions and wrong results. Some of the major troubles can be patched out of tzlocal by dropping the stupid asserts but the main problem remains that ZoneInfo is not able to parse proper TZ environment.

So please use the python base structures to use timezone instead of the broken tzlocal/ZoneInfo way.