Build arm64 multiplatform images

[dguenther]

Updates the action workflows to build images for amd64 and arm64, then create a multiplatform manifest image for them.

Changes

The builds were using QEMU, but that seemed to OOM or take 5+ hours to complete. This PR uses the Linux ARM runners that are available in public preview. The multiplatform build is based off the Docker docs.

Future Improvements

• Builds still take between ~26-40 mins to complete, up from ~20 mins with x64. If that's too slow, we could try larger ARM runners or optimizing the reth build.

• There's a lot of code duplication in the workflows -- it'd be nice to clean up, but I think it'd make this PR tough to review if it was done here.

Testing

• ✅ Images are available on ghcr.io/dguenther/node-geth:main, etc. Tested and merged this on my fork (with the repo owner changed).
• ✅ Ran node, node-geth, node-reth on Base Sepolia for ~30 secs using supervisord
• ❌ node-nethermind errors with spawnerr: command at '/app/execution-entrypoint' is not executable under supervisord -- I reproduced that issue on base/node-nethermind:main, so not related to this change. lmk if you'd like additional testing here.

[cb-heimdall]

✅ Heimdall Review Status

Requirement	Status	More Info
Reviews	✅ 1/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1

[0x00101010]

Thank you for this, would you be able to try fix nethermind build issue and also dedup the code as well? @dguenther

[dguenther]

Yep! I'll make tracking issues for those and work on them in separate PRs.