automatically setup, and always run inside of, a venv

[skyegalaxy]

Description

Before I realized I should just be running everything in a virtual environment, I ran into a lot of friction trying to set up this script and getting it to run consistently on my host.

For new contributors that gain access to these tools and the ability to start CI jobs, it would be ideal to have this "just work" out of the box for them without worrying "what's your host dependencies, what version of ubuntu or python etc are you running", etc.

Related Issues

** Is this feature dependent on any other features? Is it part of a larger project? Note here. **

Completion Criteria

** What needs to be true before we can call this "Done"? Bullet lists are appropriate. **

• A tool exists to automatically setup a venv if needed (ros-ci-setup-venv)
• invoking ros-ci-for-pr always runs the script inside a venv of some sort without needing to prepend it with uv run or start up your own venv shell

Implementation Notes / Suggestions

My recommendation and personal preference would be to use uv, but I'm not married to any one particular venv if others are strongly opinionated, so long as it works the same for everybody.

Testing Notes / Suggestions

** All features in this project need tests. Please give some input on cases that will need to be tested - and how the testing might be implemented. **

[christophebedard]

Before I realized I should just be running everything in a virtual environment

I think the simplest solution is to add the setup steps to the README: create a venv, source it, install, and then run the tool. I didn't know it wasn't already documented.

but if you really want uv, I think that's fine.