Caching behavior and cache control commands

NVS caches downloaded archives (`node*.7z`, `node*.tar.xz`, etc.) at `$NVS_HOME/cache`. Currently these files remain in the cache indefinitely even after removing an installation via `nvs rm`.

Maybe the archives should also be removed by `nvs rm`. Or maybe there should be commands for managing the cache: `nvs cache ls`, `nvs cache rm`, `nvs cache clear`.

Start by reading how `nvs rm` works and how downloaded archives are stored under `$NVS_HOME/cache`. The issue offers alternative approaches but does not decide which behavior to implement, so clarify the intended scope with maintainers before proceeding; done depends on that decision.

Written by the indexing model from the issue text.