Timezone aware datetimes

[pnuu]

With Python 3.12 we get these warnings:

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).

When running the tests, we get 107135 of them (the actual number changes depending on the run time). There are zero warnings with Python 3.11.

We need to make the datetimes timezone aware. I made a quick try, but ran into some snags that I don't have the time to tackle today:

• the code needs flake8 work
• we need to stop doing from datetime import datetime as it makes it impossible to do other imports from datetime package. Instead do import datetime as dt
• making the datetimes tz-aware I got these assertion errors: AssertionError: '2010-12-03T16:28:39' != '2010-12-03T16:28:39+00:00', so I sense we might get backwards incompatibilites within the messages