Switch to zoneinfo from pytz

[matmair]

We target 3.9 which has zoneinfo for timezone info instead of pytz.

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[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 85.33%. Comparing base (6634bc5) to head (309e323).
Report is 9 commits behind head on master.

Files with missing lines	Patch %	Lines
src/backend/InvenTree/InvenTree/helpers.py	66.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7645      +/-   ##
==========================================
+ Coverage   85.24%   85.33%   +0.08%     
==========================================
  Files        1175     1175              
  Lines       52424    52430       +6     
  Branches     2075     2078       +3     
==========================================
+ Hits        44691    44740      +49     
+ Misses       7226     7180      -46     
- Partials      507      510       +3     

Flag	Coverage Δ
backend	86.96% <80.00%> (ø)
migrations	43.18% <60.00%> (+<0.01%)	⬆️
pui	69.47% <ø> (+0.44%)	⬆️

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[SchrodingersGat]

Nice. Should we also remove pytz from the requirements?

[matmair]

@SchrodingersGat sadly not, some of our dependencies still depend on it

[matmair]

I need to figure out why CI works on my machine but not on GH

[matmair]

This is more complex than initially thought. https://blog.ganssle.io/articles/2018/03/pytz-fastest-footgun.html
I am amazed we have not had problems with pytz before.

[SchrodingersGat]

Wow, what a deep dive!

[SchrodingersGat]

@matmair it would be great to get this one closed out if you have some time to assign to it :)

[matmair]

@SchrodingersGat this is more a skill not a time issue ;-) I can look into it after sso and selection lists

[SchrodingersGat]

Ok, LMK if you are banging your head against the wall on it!

[matmair]

@SchrodingersGat can you take a look at this? Especially the change in the test assertations. Maybe I am missing something but the previous assertations seem strangely off by a few minutes.

[1337joe]

To add some specific discussions of this to add to your link above:
https://stackoverflow.com/questions/27531718/datetime-timezone-conversion-using-pytz
https://stackoverflow.com/questions/60996205/python-datetime-timezone-conversion-off-by-4-minutes

Long story short, using replace(tzinfo=... (what InvenTree was using) can make invalid assumptions, where localize(time) would try to correct for that. The old test values were the incorrect values that pytz would produce for those zone conversions.

For what it's worth, your updated test values are correct from my manual checking on: https://dateful.com/time-zone-converter

[matmair]

@SchrodingersGat ready for review and merge; I have marked it as breaking as a precaution, I do not think it should break anything

[SchrodingersGat]

@matmair seems like a minimal change overall, in the end. Thank you for looking into this one.