Use go.mod for Go version, update checkout action, and add Zig CI job

[hamidzr]

Motivation

• Ensure CI picks the repository Go version by using go.mod so workflows stay in sync with the module.
• Update actions/checkout to the newer @v4 to follow current GitHub Action recommendations and avoid incompatibilities.
• Add CI coverage for the zig-mvp subproject so the Zig MVP build is validated in automation.
• Address existing CI failures caused by hardcoded tool versions and missing Zig build verification.

Description

• Modified .github/workflows/go.yaml to replace actions/checkout@v3 with actions/checkout@v4 for Go jobs.
• Changed actions/setup-go@v5 usage to read the Go version from go.mod via go-version-file: go.mod instead of a hardcoded 1.23.
• Added a new zig-build job that sets up Zig with mlugg/setup-zig@v1 and runs zig build in the zig-mvp directory.
• Kept existing lint and test jobs, which continue to call just get-deps, just lint, and just test as before.

Testing

• No automated tests were executed locally since this change only updates CI workflow files and triggers validation when the PR is run.
• The repository CI is expected to run the lint and test jobs which execute just lint and just test respectively when the workflow triggers.
• The new zig-build job will run zig build in CI to validate the zig-mvp subproject.
• Recommended local validation commands are just check and just test, but they were not executed as part of this change.

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Codex Task

[gemini-code-assist]

Note

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