Don't store pip and uv cache files in our docker images

[igorts-git]

Description

uv and pip create a copy of everything they fetch under the /root/.cache dir. Those cached files are not used at runtime.
This cache adds about 4 GB to the docker image size.

We use the Dockerfile syntax below to avoid creating the /root/.cache/[pip|uv] dirs inside the final image:

RUN --mount=type=cache,target=/root/.cache/pip \
    --mount=type=cache,target=/root/.cache/uv \
    pip install package

Tests

Manually built a couple of variants of the docker images. Confirmed that they get smaller and still run under XPK.

Checklist

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• I have made or will make corresponding changes to the doc if needed, including adding new documentation pages to the relevant Table of Contents (toctree directive) as explained in our documentation.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[github-actions]

🤖 Hi @igorts-git, I've received your request, and I'm working on it now! You can track my progress in the logs for more details.

[github-actions]

## 📋 Review Summary

This PR correctly implements BuildKit cache mounts (--mount=type=cache) to prevent pip and uv from polluting the final Docker image with cache files. The change successfully addresses the 4 GB image size reduction goal.

🔍 General Feedback

• Cache utilization vs. image bloat: Using Docker cache mounts is the ideal solution for keeping package installation caches out of the final image. However, some pip install commands still include the --no-cache-dir flag. Removing this flag allows pip to actually populate and use the mounted cache directory during the build, which will speed up subsequent local rebuilds while continuing to keep the image small.
• Uninstall commands: Several pip uninstall commands now use the cache mount. Since uninstalling packages does not read or write to the cache, this mount is redundant and can be omitted.

[richjames0]

lgtm