Update to pydantic v2 and fix deprecated API usage.

[daniel-k]

This fixes lots of deprecration warnings in CI builds and ultimately for users as well. From now on, we will require pydantic>=2 as we now use their new API.

NB: I've piggy-backed removing the deprecated usage of datetime.utcnow() as well. This only affects our tests though.

[github-actions]

Coverage results

This is the coverage report for commit 8b8daf8

Name                                                                                Stmts   Miss  Cover   Missing
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.tox/py/lib/python3.12/site-packages/enlyze/__init__.py                                 4      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/api_clients/base.py                        65      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/api_clients/production_runs/client.py      20      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/api_clients/production_runs/models.py      51      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/api_clients/timeseries/client.py           19      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/api_clients/timeseries/models.py           34      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/auth.py                                    13      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/client.py                                  86      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/constants.py                                6      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/errors.py                                   3      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/models.py                                 108      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/validators.py                              38      0   100%
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TOTAL                                                                                 447      0   100%

4 empty files skipped.