fix: refactor datetime to remove deprecation warnings

[emmanuel-ferdman]

PR Summary

This small PR fixes the datetime deprecation warnings which you can find in the CI logs:

DeprecationWarning: datetime.datetime.utcnow() is deprecated and scheduled for removal in a future version. Use timezone-aware objects to represent datetimes in UTC: datetime.datetime.now(datetime.UTC).
    date_start = datetime.utcnow()

[emmanuel-ferdman]

Hi @fabclmnt, can you please review this small PR when you get the chance? thanks 🙌

[fabclmnt]

@emmanuel-ferdman it seems that the changes are breaking the tests.

Can you please revise the code?

[emmanuel-ferdman]

@fabclmnt CI is stable now - how can we progress from here?

[emmanuel-ferdman]

Hi @fabclmnt, sorry again for bumping but could we please finish with this small PR?