Add test suite and CI workflow

[theinfosecguy]

• Add Vitest for testing framework
• Add --skip-install CLI option for faster test execution
• Add unit tests for all lib modules (57 tests total)
• Add GitHub Actions CI workflow
• Add vitest.config.js with coverage thresholds (70% statements/lines/functions, 60% branches)

Test Structure:

• tests/unit/ - Unit tests for lib modules
• tests/integration/ - CLI integration tests

CI Workflow:

• Runs on push to main and PRs
• Tests on Node.js 18, 20, 22