Unknown token

#### Issue description:

`synp -w --source-file ./yarn.lock`

#### Are you reporting a conversion error? Please include a link to `yarn.lock` / `package-lock.json`:
```
# This file is generated by running "yarn install" inside your project.
# Manual changes might be lost - proceed with caution!

__metadata:
version: 6
cacheKey: 8
...
more thousands lines
```

Start by reproducing `synp -w --source-file ./yarn.lock` with the provided Yarn lockfile content, then identify which token causes the conversion error. Done means the reported Yarn lockfile converts successfully without an unknown-token failure and the behavior is covered by a regression test.

Written by the indexing model from the issue text.