Add `-orphans` Flag to the `list` Command

[AshokThangavel]

When a primary module is uninstalled without -r, its dependencies are often left behind in the namespace. Currently, IPM/ZPM has no way to distinguish between a module you wanted (Direct Install) and a module you needed (Dependency). Consequently, these leftover dependencies appear as "root" modules in a standard list, creating a cluttered environment where it is impossible to tell which packages are safe to remove and which are still serving a purpose.

Proposed Solution

Introduce an -orphans flag (with the alias -u for unused) to the list command to identify unreferenced, non-primary modules.

1. New Flag: list -orphans (Alias: list -u).
2. Detection Criteria: The command identifies modules that meet two conditions:

• Implicitly Installed: The module was originally brought in as a dependency, not via a direct user install command.
• Unreferenced: No other currently installed module in the namespace lists this package as a dependency.

3. Display: The command output will specifically list these "leftover" modules, allowing the user to see exactly what is no longer required by the system.

[isc-dchui]

As discussed by the IPM team, doesn't seem to fill a need that's not already covered by the history log, which will tell the user what was installed/uninstalled and when.