.github/workflows: Migrate workflows to Blacksmith runners

[blacksmith-sh]

This PR has been automatically generated by a team member in your GitHub organization using Blacksmith's Migration Wizard. This PR changes the following:

1. Your selected workflows will now run on Blacksmith's 2x faster hardware (e.g., runs-on: blacksmith-4vcpu-ubuntu-2204). Learn more about the different instances available to choose from.
2. Your jobs running on Blacksmith will now have all official GitHub and popular third-party cache actions automatically interact with our 4x faster, colocated cache. Learn more about Blacksmith's actions cache.
3. Your GitHub Actions will now actually be observable. Learn more about Blacksmith's logging and other observability features.
4. Your selected checkout steps now use Blacksmith's cached checkout action. Learn more about Git checkout caching.

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Restore a distinct Intel macOS smoke runner

These two matrix entries now select the same runner, while the invoked bun build --compile has no target override and test/install.test.ts derives its archive architecture from process.arch. Consequently, regardless of which architecture this Blacksmith runner provides, both jobs validate that same native architecture and the macOS x86-64 binary/installer loses its native smoke coverage. Use a distinct Intel-capable runner label (or retain the Intel GitHub runner) for the x86-64 row.

Useful? React with 👍 / 👎.