Handle UNIX timestamps in handle_datetime

[jvavrek]

Passing a UNIX timestamp like 1686726000.0 to handle_datetime currently gives an error, but we can parse it with datetime.fromtimestamp.

[jvavrek]

One test failure occurs on the CI but not my machine:

FAILED tests/utils_test.py::test_handle_datetime[1686726000.0] - AssertionError: assert datetime.datetime(2023, 6, 14, 7, 0) == datetime.datetime(2023, 6, 14, 0, 0)

This is almost certainly a timezone issue.

The other test failure is in isotope_qty_test.py, which I will investigate.

[markbandstra]

Sorry @jvavrek , I accidentally canceled the tests while trying to rerun them, I didn't see you had just pushed.

[jvavrek]

Sorry @jvavrek , I accidentally canceled the tests while trying to rerun them, I didn't see you had just pushed.

No problem. I only updated from main, so they were bound to fail again anyway.