Upgrade @actions/core to v3 and @actions/tool-cache to v4

These packages are now ESM-only, which is incompatible with @vercel/ncc's
CJS bundling. Switch the bundler from ncc to esbuild, set package type to
"module", update tsconfig to use node16 module resolution, and rename
jest.config.js to jest.config.cjs for CJS compatibility.

https://claude.ai/code/session_01QwnXfWH2ELHXvNgijYTeM1

Author: claude