Replace npm pack with pnpm pack in prod build script

[kofi-q]

After the upgrade to Node v20 and NPM v10, the npm pack step of our build fails for the eslint-plugin-vx package, which has a self-reference in the dependency list. Looks like we won't have the same issue wtih pnpm pack, so worth switching over to avoid #5429 and also have more tooling consistency between our dev and prod builds.

[arsalansufi]

I'm going to move this over to v4.1 for now as it's not critical for v4 and we have things in a working state