fix: dev container

[JonathanRayner]

Currently the dev container is broken, this PR fixes it by:

• Replacing deprecated sklearn package with scikit-learn
• Update docker container to run Python 3.11 (install fails due to dependency issues with Python 3.7)
• Fix pip install command for flax (was pointing to the wrong path)

Checklist

• [x] This PR fixes a minor issue (e.g.: typo or small bug) or improves the docs (you can dismiss the other checks if that's the case).
• [ ] This change is discussed in a Github issue/ discussion (please add a link).
• [ ] The documentation and docstrings adhere to the documentation guidelines.
• [ ] This change includes necessary high-coverage tests. (No quality testing = no merge!)

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