feat: add fixture lifecycle hooks

[GiHoon1123]

Closes #14

Add optional setup and teardown hooks to Fixture.create and Fixture.fromDirectory.

• run setup after files are written or copied
• run teardown before the fixture directory is removed
• keep cleanup running when a hook fails and preserve multiple errors
• keep cleanup idempotent for repeated, concurrent, and re-entrant calls
• document the new options in English and Korean

Tests: yarn test run, yarn typecheck, yarn lint, yarn format:check, yarn build