ci: workflow improvements

[rmdg88]

regarding build and tests:

• updated actions versions
• the new test stage, runs after the build, and so it uses the build cache, one is just exporting the build cache to docker
  load: true # == '--output=type=docker'
• it runs for all images
• stage does: mounts container, checks health, runs pytest, cleanup
• adds images tests for released, -cpu and -cu* (commented out now,maybe not needed anymore)

regarding releases:

• adds docling packages versions to changelog, from uv.lock

ref #302

[github-actions]

✅ DCO Check Passed

Thanks @rmdg88, all your commits are properly signed off. 🎉

[mergify]

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• title ~= ^(fix|feat|docs|style|refactor|perf|test|build|ci|chore|revert)(?:\(.+\))?(!)?:

[dolfim-ibm]

lgtm

[dosubot]

Documentation updates

Checked 2 published document(s). No updates required.

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