test: migrate tests to cross-runtime node:test

[BottieMcBotface]

Summary

Migrate every *.bun.test.ts file in this repo to *.test.ts using node:test plus @std/expect, so the test suite runs under Bun, Deno, and Node 24+ from one set of source files. Pure mechanical migration, no feature work.

What's in scope

• Rename all 12 *.bun.test.ts files to *.test.ts:
  • examples/runtime-matrix.test.ts
  • src/fs/getFileInfo.test.ts
  • src/gh/gh.test.ts
  • src/git/git.test.ts
  • src/script/FileLogging.test.ts
  • src/script/OutputContext.test.ts
  • src/script/Script.test.ts
  • src/script/parseScriptArgs.test.ts
  • src/script/splitCommandLines.test.ts
  • src/sh/run.test.ts
  • src/utils/utils.test.ts
  • tools/getPathToRepoRoot.test.ts
• Replace import { test } from 'bun:test' with node:test (or the local shim) and import { expect } from '@std/expect'.
• Add src/test/testlib.ts: a small shim on top of node:test that adds describe / beforeEach / afterEach semantics with sequential scheduling so the existing cleanup-heavy test files keep working.
• Add src/test/cleanup.ts: the withCleanup() helper used by the new tests.
• package.json: add @std/assert and @std/expect as devDependencies (via the @jsr/std__assert / @jsr/std__expect bridge), add the check / fix / test scripts. The test script splits the fast Bun suite from the heavy runtime-matrix suite using the same --timeout 30000 --max-concurrency 1 knobs CI already uses.
• deno.jsonc: add @std/assert and @std/expect to the imports map, drop the stale *.bun.test.ts / *.bun.ts exclude + check.exclude blocks, and add publish.exclude with src/test and **/*.test.ts so no test sources ship to JSR.
• .github/workflows/ci.yml: update both Bun test steps to reference the renamed examples/runtime-matrix.test.ts.

What's out of scope

This PR is intentionally narrow. It unblocks the wait-for rebuild (PRs 2-4), but does not touch:

• Anything under src/wait/.
• src/utils/groupArgs.ts / groupArgs.demo.ts — those move to @axhxrx/args in PR 2.
• claude-summarize.demo.* — can come in a later PR if wanted.
• wait-for.ts / wait-for.test.ts / wait-for.spec.md — those move to @axhxrx/wait-for in PR 4.

Verification

Verified in a fresh off-tree directory (outside the megarepo workspace) to avoid this session's worktree-specific Deno workspace and Bun hoisting quirks:

• bun run test — 207 / 207 pass (Bun + Deno + Node, run sequentially).
• bun run check — deno check && deno lint && bun tsc --noEmit && dprint check all clean. 61 files checked.
• deno publish --dry-run --allow-dirty — no *.test.ts files and no src/test/ files ship to JSR.

Code review (via bun review/main.ts run) round 2 returned no actionable findings after the three round-1 issues (CI workflow paths, default Bun test script, Deno publish excludes) were fixed.

[masonmark]

This one looks like the 🤖🤖🤖 went off the rails a little bit, so I don't want to bother reviewing this. I'm just gonna close it.

I'll take a look myself later; might let them take another crack at it after giving them a couple clean examples.