Consider server timezone on _get_timezone_offset instead of django's settings

[iwalucas]

DatabaseScheduler class consider's django timezone calculations to offset hour, but beat uses server's so that creates a situation where some tasks are excluded from running hours

Report: #885

[Copilot]

Pull Request Overview

This PR updates the _get_timezone_offset method so that it leverages the server's timezone rather than Django's timezone settings.

• Removed dependency on django.utils.timezone
• Obtains the server time via aware_now() and retrieves its timezone using ZoneInfo

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.17%. Comparing base (87c0597) to head (70d34ac).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #886      +/-   ##
==========================================
+ Coverage   88.07%   88.17%   +0.09%     
==========================================
  Files          32       32              
  Lines        1006     1006              
  Branches      104      104              
==========================================
+ Hits          886      887       +1     
  Misses        101      101              
+ Partials       19       18       -1     

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[auvipy]

I was thinking if you can add some additional tests to verify the changes, and check if it creates any regresion

[jennifer-richards]

Suggest a minor rephrasing in the code.

[jennifer-richards]

The tzinfo class does not define __str__. It would be better to use server_time.tzinfo.tzname() which is guaranteed to exist.

There's no guarantee ZoneInfo will know what to do with the tzname(), though, so this won't work with obscure timezone implementations. (Edit: or with obscure zones not known to ZoneInfo. Either of these cases will probably break Django, so I don't think that this is a problem, just pointing it out.)

[auvipy]

@alirafiei75 can you please have another look