Error: Failed to execute ip netns add

I'm running in a Docker container, which does not (cannot) have `ip` installed.

```bash
user@test-workspace-88b1c24e:/workspace/test-workspace$ sudo ~user/.cargo/bin/httpjail --js "r.host === 'github.com'" -- hello
21:58:40.666 ERROR httpjail::sys_resource: Failed to cleanup resource on drop: Failed to execute ip netns del
Error: Failed to execute ip netns add

Caused by:
No such file or directory (os error 2)
```

I don't think this can ever work within a Docker container.

Reproduce the `httpjail --js ... -- hello` command in a Docker container without `ip`, then inspect the network-namespace setup reached by that entry point. Confirm whether this environment is supported and establish the expected behavior when the required command is unavailable.

Written by the indexing model from the issue text.