uenv image inspect is more flexible

[bcumming]

This adds support for the most requested user-convenience feature

Namely "how do I see which views are in a uenv before starting it?"

The default output for uenv image inspect now shows the mount point and views of a uenv:

$ uenv image inspect namde/3.0:v1
namd/3.0:v1@eiger%zen2 mount at /user-environment
views:
  spack: configure spack upstream
  namd:
  modules: activate modules
  develop:

The --format option is still supported, but now it has more options:

$ uenv image inspect --format='{name}/{version} with metadata {meta}' namd/3.0:v1
namd/3.0 with metadata /home/bcumming/.uenv/repo/images/cd8d842d108f2eb1b69ca24402d69734f4ad9164f248cda804a5a78305be6f96/meta

And a new --json option will dump everything we know in JSON format for easier integration with scripts:

$ uenv image inspect --json namd/3.0:v1
{
  "date": "2025-05-21 15:31:07",
  "description": "NAMD: Scalable Molecular Dynamics",
  "digest": "cd8d842d108f2eb1b69ca24402d69734f4ad9164f248cda804a5a78305be6f96",
  "id": "cd8d842d108f2eb1",
  "meta": "/home/bcumming/.uenv/repo/images/cd8d842d108f2eb1b69ca24402d69734f4ad9164f248cda804a5a78305be6f96/meta",
  "mount": "/user-environment",
  "name": "namd",
  "path": "/home/bcumming/.uenv/repo/images/cd8d842d108f2eb1b69ca24402d69734f4ad9164f248cda804a5a78305be6f96",
  "sqfs": "/home/bcumming/.uenv/repo/images/cd8d842d108f2eb1b69ca24402d69734f4ad9164f248cda804a5a78305be6f96/store.squashfs",
  "system": "eiger",
  "tag": "v1",
  "uarch": "zen2",
  "version": "3.0",
  "views": [
    {
      "description": "configure spack upstream",
      "name": "spack"
    },
    {
      "description": "",
      "name": "namd"
    },
    {
      "description": "activate modules",
      "name": "modules"
    },
    {
      "description": "",
      "name": "develop"
    }
  ]
}

Note that this "simple" feature required some long-overdue refactoring, hence the number of files touched to implement it.