chore(ci): retry transient module and Docker Hub fetches (PIPE-1058, PIPE-1092)

[Dylan-M]

Proposed Change

• Retries Go module fetches on transient proxy/network errors via a shared .github/scripts/retry.sh, wrapping go mod download, make install-tools, and the GoReleaser pre-build hook. The wrapper retries only on a transient-network signature, so a real build failure still fails immediately. (PIPE-1058)
• Removes the QEMU/buildx setup from the split build legs. Those legs only cross-compile Go binaries, and the images are built in the merge-build job. The setup only added a Docker Hub pull that could time out, the exact pull that failed originally. (PIPE-1092)
• The merge-build job does build the images. It now pre-pulls and pins the QEMU and buildkit images through the retry wrapper, so a transient Docker Hub blip during setup no longer fails the build. (PIPE-1092)

Checklist

• Changes are tested
• CI has passed

[Dylan-M]

• chore(ci): retry transient module and Docker Hub fetches (PIPE-1058, PIPE-1092) #267 👈 (View in Graphite)
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