support listing/removing multiple cached versions of the same package

opensrc already caches sources in versioned paths on disk, e.g.

~/.opensrc/repos/<host>/<owner>/<repo>/<version>/

So multiple versions of the same package can already exist side by side physically.

What seems missing is index / CLI support for that case. Right now package entries appear to collapse to one entry per name + registry, which makes multi-version caches hard to inspect and manage.

This would be especially useful in monorepos / migration work where multiple exact versions matter at the same time.

Example

opensrc path zod@3.25.76
opensrc path zod@4.3.6
opensrc list

Expected: both cached versions show up in list, and remove can target an exact version when multiple are cached.

I’m not suggesting opensrc should model migration relationships (from / to) — just that if multiple versions already exist on disk, the index and CLI should expose that cleanly too.