Doesn't work in python 3.10

Description of Bug

Python API crashes on python 3.10, since it uses timezone.UTC, which is an alias that was only introduced in 3.11.

Steps To Reproduce

Steps to reproduce the behavior:

1. Try running it on 3.10

Expected behavior

Runs correctly

Actual Behaviour

    from simvue.config.user import SimvueConfiguration
../../../Library/Caches/pypoetry/virtualenvs/simvue-moose-SyxDCI6N-py3.10/lib/python3.10/site-packages/simvue/config/user.py:39: in <module>
    from simvue.eco.config import EcoConfig
../../../Library/Caches/pypoetry/virtualenvs/simvue-moose-SyxDCI6N-py3.10/lib/python3.10/site-packages/simvue/eco/__init__.py:11: in <module>
    from .emissions_monitor import CO2Monitor as CO2Monitor
../../../Library/Caches/pypoetry/virtualenvs/simvue-moose-SyxDCI6N-py3.10/lib/python3.10/site-packages/simvue/eco/emissions_monitor.py:41: in <module>
    class CO2Monitor(pydantic.BaseModel):
../../../Library/Caches/pypoetry/virtualenvs/simvue-moose-SyxDCI6N-py3.10/lib/python3.10/site-packages/simvue/eco/emissions_monitor.py:82: in CO2Monitor
    _last_local_write = pydantic.PrivateAttr(datetime.datetime.now(tz=datetime.UTC))
E   AttributeError: module 'datetime' has no attribute 'UTC'

Start with simvue/eco/emissions_monitor.py, at the CO2Monitor definition shown in the traceback, and reproduce the import failure under Python 3.10. Check the project's existing tests or test setup for supported Python versions. Done means the Python API imports and runs correctly on Python 3.10 without breaking newer supported versions.