Fix handling of time series with mixed timezone offsets

[stijnvanhoey]

See #67 for the discussion. This PR handles the request of a custom timezone over a period with mixed timezone offsets. Previously a warning was raised by Pandas and the timestamps were not parsed as pandas Timestamps.

[github-actions]

👈 Launch a binder notebook on branch fluves/pywaterinfo/SVH-pandas-warning

[johanvdw]

Seems ok, but just a heads up that we may have to switch away from pytz in the future

https://github.com/stub42/pytz/blob/master/src/README.rst#issues--limitations

This project is in maintenance mode. Projects using Python 3.9 or later are best served by using the timezone functionaly now included in core Python and packages that work with it such as tzdata.

[stijnvanhoey]

Seems ok, but just a heads up that we may have to switch away from pytz in the future

https://github.com/stub42/pytz/blob/master/src/README.rst#issues--limitations

This project is in maintenance mode. Projects using Python 3.9 or later are best served by using the timezone functionaly now included in core Python and packages that work with it such as tzdata.

Jup, good point. As we heavily rely on Pandas for the (element-wise) conversion of timezones, we follow the developments on their side. See pandas-dev/pandas#59089 as pytz will be an optional dependency in one of the following releases. Note also that we have some tests already relying on the native timezone implementation (e.g. https://github.com/fluves/pywaterinfo/blob/master/tests/test_waterinfo.py#L307)

[stijnvanhoey]

@binomaiheu is it possible that on the current requests to KIWIS all headers get a no-cache property, e.g. 'Cache-Control': 'public,max-age=0,no-cache' which was previously not the case?

[binomaiheu]

Hmm, we checked, but at first sight, the cache header config of the KiWIS API itself doesn't seem to have changed. Checking with the network admins if this could be due to firewall configuration changes...

[stijnvanhoey]

Note that the unit tests are currently failing as I have to request a new HIC token for running the unit tests.

[stijnvanhoey]

HIC account update was succesfull. @binomaiheu let me now if the caching on the reverse proxy would been adjusted. I'm merging this PR now