fix: clean dnf/yum cache after libicu install in Lambda runtime images (#2594)

[normj]

Issue #, if available

Fixes #2594

Description of changes

The base stage of every published Lambda runtime Dockerfile installs libicu via dnf without cleaning the package-manager cache:

FROM $AMAZON_LINUX AS base
RUN dnf install libicu-67.1-7.amzn2023.0.4.<arch> --assumeyes

Because the final published image stage is FROM base, it inherits that cache layer, baking roughly 170 MB of dnf/yum repository metadata into the shipped image (the .solv/.solvx solver caches and filelists.xml.gz). Deleting the cache in a downstream layer cannot reclaim those bytes — the whiteout only hides them while the earlier layer still carries them.

This PR cleans the cache in the same RUN instruction that installs libicu, so the metadata never lands in the committed layer:

RUN dnf install libicu-67.1-7.amzn2023.0.4.<arch> --assumeyes && \
    dnf clean all && \
    rm -rf /var/cache/dnf /var/cache/yum

Although the issue was filed against net10/arm64, the same uncleaned install exists in every published runtime Dockerfile, so the fix is applied across all eight:

Version	amd64	arm64
net8	✅	✅
net9	✅	✅
net10	✅	✅
net11	✅	✅

No runtime behavior changes — this only removes build-time package-manager cache that is dead weight at runtime, reducing image size and pull times for downstream consumers.

Checklist

• I have updated the changelog with a description of my changes (if applicable)
• I have read the CONTRIBUTING document
• Local run of the build and tests pass

License

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.