Update T3: use a custom .venv

[LennyN95]

To prevent any conflicts, we advice for every model to create a new virtual environment for the model and all model dependencies, separate from the mhubio virtual environment.

A custom venv can easily be created and used with uv:

# create custom venv
uv venv -p 3.10 .venv310

# install dependencies in custom venv
uv pip install -p .venv38/ numpy==2.0.0

# use custom venv
uv run -p .venv38/ python main.py