feat: 搭建单元测试基础设施 — Bun test runner + 示例测试

添加 bunfig.toml 配置、test script，以及三组示例测试：
- src/utils/array.ts (intersperse, count, uniq)
- src/utils/set.ts (difference, intersects, every, union)
- packages/color-diff-napi (ansi256FromRgb, colorToEscape, detectLanguage 等)

41 tests, 0 failures.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

TODO.md

@@ -21,5 +21,5 @@
 - [ ] 冗余代码检查
 - [x] git hook 的配置
 - [ ] 代码健康度检查
-- [ ] 单元测试基础设施搭建 (test runner 配置)
+- [x] 单元测试基础设施搭建 (test runner 配置)
 - [ ] CI/CD 流水线 (GitHub Actions)