Wind 928c57db41
save: print to stderr for bytestream (#13422)
# Description
Fixes: #13260 

When user run a command like this:
```nushell
$env.FOO = " New";
$env.BAZ = " New Err";
do -i {nu -n -c 'nu --testbin echo_env FOO; nu --testbin echo_env_stderr BAZ'} | save -a -r save_test_22/log.txt
```

`save` command sinks the output of previous commands' stderr output. I
think it should be `stderr`.

# User-Facing Changes
```nushell
$env.FOO = " New";
$env.BAZ = " New Err";
do -i {nu -n -c 'nu --testbin echo_env FOO; nu --testbin echo_env_stderr BAZ'} | save -a -r save_test_22/log.txt
```
The command will output ` New Err` to stderr.

# Tests + Formatting
Added 2 cases.
2024-07-31 18:19:35 +02:00
..