`rad cob` outputs error to stdout, not stderr — heartwood

$ rad cob show --repo $(rad .) --type xyz.radicle.patch --object README.md >/dev/null
$ rad cob show --repo $(rad .) --type xyz.radicle.patch --object README.md 2>/dev/null
✗ Error: revspec 'README.md' not found; class=Reference (4); code=NotFound (-3)

Outputting errors to stdout makes the output unreliable for scripting.

I haven’t checked the rest of the CLI, so I don’t know whether it’s just rad cob or if it’s a more systemic problem. Either way, it would be a good thing if this was corrected. The more globally (if needed), the better.