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

.changeset/add-effect-bun-test.md

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+---
+"@effect/bun-test": minor
+---
+
+Add `@effect/bun-test` package — same API surface as `@effect/vitest`
+(`it.effect`, `it.scoped`, `it.live`, `it.scopedLive`, `it.layer`, `it.prop`,
+`flakyTest`, …) but backed by Bun's native `bun:test` runner. Closes #5964.

packages/bun-test/CHANGELOG.md

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+# @effect/bun-test

packages/bun-test/LICENSE

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+MIT License
+
+Copyright (c) 2023 Effectful Technologies Inc
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

packages/bun-test/README.md

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+# @effect/bun-test
+
+A set of helpers for testing [Effect](https://effect.website) programs with
+Bun's native [`bun:test`](https://bun.sh/docs/cli/test) runner.
+
+The API mirrors [`@effect/vitest`](https://www.npmjs.com/package/@effect/vitest)
+(`it.effect`, `it.scoped`, `it.live`, `it.scopedLive`, `it.layer`, `it.prop`,
+`flakyTest`, …) but runs under Bun's built-in test runner — useful when you
+already use Bun as your runtime and want to avoid pulling in Vitest.
+
+## Installation
+
+```sh
+bun add -d @effect/bun-test
+```
+
+## Usage
+
+```ts
+import { describe, expect, it, layer } from "@effect/bun-test"
+import { Context, Effect, Layer } from "effect"
+
+class Foo extends Context.Tag("Foo")<Foo, "foo">() {
+  static Live = Layer.succeed(Foo, "foo")
+}
+
+it.effect("plain effect test", () =>
+  Effect.sync(() => expect(1).toEqual(1))
+)
+
+describe("with a shared layer", () => {
+  layer(Foo.Live)((it) => {
+    it.effect("has Foo in context", () =>
+      Effect.gen(function* () {
+        const foo = yield* Foo
+        expect(foo).toEqual("foo")
+      })
+    )
+  })
+})
+```
+
+Run with:
+
+```sh
+bun test
+```
+
+## What's supported
+
+| Helper | Status |
+| --- | --- |
+| `it.effect` / `it.scoped` / `it.live` / `it.scopedLive` | ✅ |
+| `.skip`, `.skipIf`, `.runIf`, `.only`, `.each`, `.fails` | ✅ |
+| `.prop` (fast-check integration) | ✅ |
+| `layer(...)` / nested `it.layer(...)` | ✅ |
+| `flakyTest` | ✅ |
+| `addEqualityTesters` (Effect `Equal.equals` integration) | ⚠️ no-op — see below |
+
+### Differences from `@effect/vitest`
+
+Bun's test runner does not expose all of Vitest's APIs. The notable gaps:
+
+- **`addEqualityTesters`** is a no-op — `bun:test`'s `expect` does not yet
+  expose `addEqualityTesters`. Use Effect's `Equal.equals` directly (or the
+  helpers in `@effect/bun-test/utils`) when comparing values that implement the
+  `Equal` trait.
+- **`TestContext`** — Vitest passes a `TestContext` to each test fn (with
+  `signal`, `onTestFailed`, `onTestFinished`, etc.). `bun:test` doesn't, so the
+  context passed to your Effect tests is a minimal stub. `signal` is a fresh
+  `AbortController().signal`; `onTestFailed` / `onTestFinished` register
+  best-effort callbacks invoked after the Effect completes.
+- **`scopedFixtures`** (Vitest's `it.scoped(fixtures)`) is not provided — Bun
+  has no fixture system.
+
+## License
+
+MIT

packages/bun-test/bunfig.toml

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+[test]
+root = "./test"

packages/bun-test/docgen.json

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+{
+  "$schema": "../../node_modules/@effect/docgen/schema.json",
+  "srcLink": "https://github.com/Effect-TS/effect/tree/main/packages/bun-test/src/",
+  "exclude": [
+    "src/internal/**/*.ts"
+  ],
+  "examplesCompilerOptions": {
+    "noEmit": true,
+    "strict": true,
+    "skipLibCheck": true,
+    "moduleResolution": "Bundler",
+    "module": "ES2022",
+    "target": "ES2022",
+    "lib": [
+      "ES2022",
+      "DOM"
+    ],
+    "paths": {
+      "effect": [
+        "../../../effect/src/index.js"
+      ],
+      "effect/*": [
+        "../../../effect/src/*.js"
+      ]
+    }
+  }
+}

packages/bun-test/package.json

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+{
+  "name": "@effect/bun-test",
+  "version": "0.0.0",
+  "type": "module",
+  "license": "MIT",
+  "description": "A set of helpers for testing Effects with Bun's bun:test runner",
+  "homepage": "https://effect.website",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/Effect-TS/effect.git",
+    "directory": "packages/bun-test"
+  },
+  "bugs": {
+    "url": "https://github.com/Effect-TS/effect/issues"
+  },
+  "publishConfig": {
+    "access": "public",
+    "provenance": true,
+    "directory": "dist",
+    "linkDirectory": false
+  },
+  "exports": {
+    "./package.json": "./package.json",
+    ".": "./src/index.ts",
+    "./*": "./src/*.ts",
+    "./internal/*": null
+  },
+  "scripts": {
+    "build": "pnpm build-esm && pnpm build-annotate && pnpm build-cjs && build-utils pack-v3",
+    "build-esm": "tsc -b tsconfig.build.json",
+    "build-cjs": "babel build/esm --plugins @babel/transform-export-namespace-from --plugins @babel/transform-modules-commonjs --out-dir build/cjs --source-maps",
+    "build-annotate": "babel build/esm --plugins annotate-pure-calls --out-dir build/esm --source-maps",
+    "check": "tsc -b tsconfig.json",
+    "test": "bun test",
+    "coverage": "bun test --coverage"
+  },
+  "peerDependencies": {
+    "effect": "workspace:^"
+  },
+  "devDependencies": {
+    "@types/bun": "^1.1.0",
+    "effect": "workspace:^"
+  }
+}