Fix Go-era CI fast checks

[jmcte]

Summary

• Replace stale Bats and deleted shell test references in the fast CI entrypoint.
• Validate the current Go-based repository with shellcheck, Go module verification, vet, race tests, and a binary build.
• Install Go in PR and extended validation jobs before running the Go-era script on self-hosted runners.

Governing Issue

Closes #77

Validation

• Relevant local checks passed: bash scripts/ci/run-fast-checks.sh
• Relevant local checks passed: GOMODCACHE=/private/tmp/machete-gomodcache GOCACHE=/private/tmp/machete-gocache bash scripts/ci/run-extended-validation.sh
• Required PR checks are expected to satisfy CI Gate
• Skipped checks are explained below: no checks were skipped locally.

Bootstrap Governance

• Changes are scoped to the linked issue
• Contributor or PR guidance changes are reflected in CONTRIBUTING.md, .github/PULL_REQUEST_TEMPLATE.md, and docs/bootstrap/onboarding.md when applicable: not applicable, CI script implementation only.
• PR author enabled auto-merge where GitHub allows it, or GitHub plan-limit evidence/unavailable reason is recorded and the fallback merge-readiness policy applies: auto-merge is unsafe until GitHub attaches executable PR checks.
• No real secrets, runtime auth, or machine-local env files are committed

Merge Automation

• PR author enabled auto-merge with gh pr merge --auto --squash, or the reason it is unavailable/unsafe is noted below: auto-merge is unsafe until the PR workflow attaches checks; fallback merge-readiness requires local validation plus a clean live PR state.

Notes

• The previous script sourced scripts/ci/lib/bats.sh and ran tests/*, but those files were removed during the Go migration.
• A manual Extended Validation dispatch on the first revision reached the updated script and showed the self-hosted runner did not have go preinstalled, so this PR also adds actions/setup-go@v5.

[pheidon]

Requesting changes: this PR makes scripts/ci/run-fast-checks.sh depend on Go tooling, but the repository does not contain go.mod or Go source files, so the new fast-check path will fail immediately on , , , and . Please either add the Go module and sources that these commands target, or keep the fast-check script aligned with the repo's actual shell-based layout.

[pheidon]

Approved. The fast-check path now matches the repository layout: go.mod and cmd/machete exist, and the workflows install Go before invoking the new Go-based checks.