feat(bun-test): add @effect/bun-test package

[emilienbidet]

Summary

Adds a new @effect/bun-test workspace package that mirrors the @effect/vitest
API surface (it.effect, it.scoped, it.live, it.scopedLive, it.layer,
it.prop, flakyTest, layer, …) but runs on Bun's built-in
bun:test runner instead of Vitest.

Closes #5964.

Why

Quoting #5964: Bun's test runner is significantly faster than Vitest, and the
Vitest dependency of @effect/vitest is a thin wrapper around it() and
describe() — the actual Effect test machinery (TestClock, TestServices,
fast-check integration) is runner-agnostic. This PR ports that thin wrapper
to bun:test so users on Bun can avoid pulling in Vitest entirely.

What's in the package

packages/bun-test/ is laid out exactly like packages/vitest/:

• src/index.ts — public API, types, re-exports of bun:test primitives
• src/internal/internal.ts — Effect runner + tester/layer/prop wrappers
• src/utils.ts — assertion helpers (copied from @effect/vitest utils.ts,
  vassert.instanceOf swapped for node:assert)
• test/index.test.ts — ported from packages/vitest/test/index.test.ts
• tsconfig.*, docgen.json, bunfig.toml, package.json, README.md,
  LICENSE

A changeset is included (.changeset/add-effect-bun-test.md).

Differences from @effect/vitest

Bun's test runner has a smaller surface than Vitest. The PR documents these
gaps in the package README; they were not papered over with runtime shims:

• addEqualityTesters is a no-op — bun:test's expect has no
  addEqualityTesters API. Effect's Equal.equals is exposed via the
  package-level helpers in @effect/bun-test/utils (assertEquals, etc.).
• TestContext is synthesised inside the test wrapper rather than passed
  in by the runner, because bun:test doesn't pass a context object. It
  exposes a fresh signal: AbortSignal and best-effort onTestFinished /
  onTestFailed callbacks invoked after the Effect resolves.
• scopedFixtures (vitest's fixture system) is not provided.
• re-export from \"bun:test\" doesn't work in Bun (1.2.x), so the public
  primitives are re-exported via const bindings rather than export *.

Test plan

• pnpm install at the workspace root resolves cleanly
• pnpm --filter=@effect/bun-test check passes
• bun test inside packages/bun-test is green
  • 32 pass, 6 skip, 0 fail (the skips are the test file's deliberate
    it.skip/it.skipIf(true) cases)
• Maintainers to decide whether CI should grow a Bun job for this package

Notes for review

• One Bun-specific tweak in test/index.test.ts: the layer > release test
  had its trailing afterAll(...) reordered so it runs after the layer's
  own afterAll (Bun runs afterAll hooks in registration order; Vitest's
  ordering happened to release the scope before the assertion).
• The it.scopedLive.fails("interrupts on timeout", ...) test from the Vitest
  suite was dropped because Bun doesn't expose the equivalent of Vitest's
  onTestFailed hook with a fiber-interrupt handle.
• No upstream files outside packages/bun-test/, .changeset/, and
  pnpm-lock.yaml were touched.

[changeset-bot]

🦋 Changeset detected

Latest commit: 3f8d6e8

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@effect/bun-test	Minor

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