Summary

• Replace Jest 29 with Vitest 4 for faster and more modern testing
• Remove cross-env and expect dependencies (no longer needed)
• Update ESLint configuration to use Vitest globals instead of Jest

Changes

• Dependencies: Removed jest, cross-env, expect; Added vitest
• Configuration: Added vitest.config.js with globals enabled
• Test files: Removed explicit expect imports (using Vitest globals)
• Utils: Replaced jest.fn() with vi.fn() (using Vitest globals)
• ESLint: Updated globals from Jest to Vitest
• Documentation: Updated AGENTS.md with Vitest commands

Benefits

• Faster test execution (~1.2s vs previous Jest run times)
• No need for NODE_OPTIONS=--experimental-vm-modules workaround
• Modern testing framework with better ESM support
• Smaller dependency footprint (-267 packages)