Epic: nerdctl namespace issues

### Description

- [ ] both `namespace update` and `namespace inspect` with non-existing namespaces (with possibly invalid names) do not error, and return results (test for: " ", "_", "∞", "")
- [ ] if multiple identifiers are passed to `inspect`, it will return a `len(array) > 1` of bogus results
- [ ] `namespace update` should enforce the presence of a `--label`, as updating without any does not do anything
- [ ] `namespace list` should support a format argument
- [ ] `namespace inspect`, `namespace remove` and `namespace update` should have `completion` on namespaces names
- [ ] `namespace inspect` format support is questionnable: by default, inspect outputs valid json, but with --format json, it will output a stream of json entries - table and wide are not supported
- [ ] `namespace inspect` should at least have the same information available on `namespace list` (inc. number of volumes, containers, labels, etc)

### Steps to reproduce the issue

_No response_

### Describe the results you received and expected

na

### What version of nerdctl are you using?

main

### Are you using a variant of nerdctl? (e.g., Rancher Desktop)

None

### Host information

_No response_