Warn when an unsupported Python version is encountered

[zanieb]

I rebased #2757 then realized that we want to implement this for more than uv venv.

Closes #2587
Closes #2757

❯ cargo run -q -- pip install -p /Users/mz/bin/python3.7 anyio
warning: uv is only compatible with Python 3.8+, found Python 3.7.17.
Audited 1 package in 84ms

❯ cargo run -q -- venv -p /Users/mz/bin/python3.7
warning: uv is only compatible with Python 3.8+, found Python 3.7.17.
Using Python 3.7.17 interpreter at: /Users/mz/bin/python3.7
Creating virtualenv at: .venv
Activate with: source .venv/bin/activate