feat(jco): add node js assert impl

[vados-cosmonic]

This PR does a few things at once:

1. Adds node:assert as an impl for the builtin node bindings
2. Adds unenv to reuse their built in implementations (e.g. buffer, urlstring)
3. Adds tests that are API specific
4. Adds tests that are from the guest perspective (so incoming code can look like "normal" NodeJS code)