Add Fourier CLI

[pepicrft]

Short description 📝

With the goal of improving the contributor's experience, I'm evolving our already-large Rakefile into a CLI with streamlined commands to interact with the projects and setting up the environment. This PR configures a new Ruby CLI in the repository, bin/fourier (in Ruby), and adds a new GitHub workflow to run its tests. The goal with this effort is also to ensure that our workflows are tested and that work deterministically.

Bear in mind that I'm not moving the current Rake tasks. I'll gradually do that in future PRs.

I'm taking the opportunity to migrate the project to Ruby 3, which was released today

Checklist ✅

• The code architecture and patterns are consistent with the rest of the codebase.
• A developer other than the author has verified that the changes work as expected.
• The changes have been tested following the documented guidelines.
• The CHANGELOG.md has been updated to reflect the changes. In case of a breaking change, it's been flagged as such.
• In case the PR introduces changes that affect users, the documentation has been updated.