Support use-node-version from .npmrc

Documented here: https://pnpm.io/npmrc#use-node-version

example:

```bash
use-node-version=22.9.0
```

since .npmrc is not a leagcy file, it should be supported out of the box, with no flags, no `.tool-versions` required.

Start by tracing the plugin's existing version-resolution entry point and compare it with the documented .npmrc use-node-version setting shown in the issue. The work is done when a project containing use-node-version=22.9.0 selects that Node.js version without flags or a .tool-versions file, with coverage for the documented example.

Written by the indexing model from the issue text.