Add support for nub package manager

[2u841r]

Describe the feature

Add nub (https://github.com/nubjs/nub, site: https://nubjs.com) as a supported package manager option, alongside npm/pnpm/yarn/bun/deno/vlt/vp.

nub is a Rust-based Node.js toolkit (install/add/run/exec commands, workspace support) claiming notable speed gains over pnpm/npx. Adding it would let npmx show install/run commands in nub's syntax for users on that toolchain.

Already have a working implementation on branch feat/nub-package-manager if useful as a starting point.

Additional information

• Would you be willing to help implement this feature?

Final checks

• Read the contribution guide.
• Check existing issues.