test: restore missing NFT `exports*` unit fixtures (#97459)
### What?
Restores the missing `node_modules` fixtures for the `exports`,
`exports-fallback`,
`exports-only` and `exports-path` cases in `turbopack-tracing`'s NFT
unit test suite
(`tests/unit.rs`), and enables the two that pass as-is (`exports-only`,
`exports-path`).
Co-authored-by: vercel-fleet[bot] <308483924+vercel-fleet[bot]@users.noreply.github.com>
