Add something like `output_to_str` for `Output`

Doing this with Inspect.to_str is not great:
```
"{status: (Err (Other "Non-zero exit code: 1")), stderr: [102, 105, 110, 100, 58, 32, 226, 128, 152, 119, 119, 119, 47, 98, 117, 105, 108, 100, 47, 98, 117, 105, 108, 116, 105, 110, 115, 226, 128, 153, 58, 32, 78, 111, 32, 115, 117, 99, 104, 32, 102, 105, 108, 101, 32, 111, 114, 32, 100, 105, 114, 101, 99, 116, 111, 114, 121, 10], stdout: []}"
```