nushell#10851)

# Description
Fixes: nushell#10271

Given the following script:
```shell
# test.sh
echo aaaaa
echo bbbbb 1>&2
echo cc
```

This pr makes the following command possible:
```nushell
bash test.sh err> /dev/null | lines | each {|line| $line | str length}
```


## General idea behind the change:
When nushell redirect stderr message to external file
1. it take stdout of external stream, and pass this stream to next
command, so it won't block next pipeline command from running.
2. relative stderr stream are handled by `save` command

These two streams are handled separately, so we need to delegate a
thread to `save` command, or else we'll have a chance to hang nushell,
we have meet a similar before: nushell#5625.

### One case to consider
What if we're failed to save to an external stream? (Like we don't have
a permission to save to a file)?
In this case nushell will just print a waning message, and don't stop
the following scripts from running.

# User-Facing Changes
## Before
```nushell
❯ bash test2.sh err> /dev/null | lines | each {|line| $line | str length}
aaaaa
cc
```

## After
```nushell
❯ bash test2.sh err> /dev/null | lines | each {|line| $line | str length}
╭───┬───╮
│ 0 │ 5 │
│ 1 │ 2 │
╰───┴───╯
```

BTY, after this pr, the following commands are impossible either, it's
important to make sure that the implementation doesn't introduce too
much costs:
```nushell
❯ echo a e> a.txt e> a.txt
Error:   × Can't make stderr redirection twice
   ╭─[entry #1:1:1]
 1 │ echo a e> a.txt e> a.txt
   ·                 ─┬
   ·                  ╰── try to remove one
   ╰────

❯ echo a o> a.txt o> a.txt
Error:   × Can't make stdout redirection twice
   ╭─[entry nushell#2:1:1]
 1 │ echo a o> a.txt o> a.txt
   ·                 ─┬
   ·                  ╰── try to remove one
   ╰────
```

nushell#10851)

# Description
Fixes: nushell#10271

Given the following script:
```shell
# test.sh
echo aaaaa
echo bbbbb 1>&2
echo cc
```

This pr makes the following command possible:
```nushell
bash test.sh err> /dev/null | lines | each {|line| $line | str length}
```


## General idea behind the change:
When nushell redirect stderr message to external file
1. it take stdout of external stream, and pass this stream to next
command, so it won't block next pipeline command from running.
2. relative stderr stream are handled by `save` command

These two streams are handled separately, so we need to delegate a
thread to `save` command, or else we'll have a chance to hang nushell,
we have meet a similar before: nushell#5625.

### One case to consider
What if we're failed to save to an external stream? (Like we don't have
a permission to save to a file)?
In this case nushell will just print a waning message, and don't stop
the following scripts from running.

# User-Facing Changes
## Before
```nushell
❯ bash test2.sh err> /dev/null | lines | each {|line| $line | str length}
aaaaa
cc
```

## After
```nushell
❯ bash test2.sh err> /dev/null | lines | each {|line| $line | str length}
╭───┬───╮
│ 0 │ 5 │
│ 1 │ 2 │
╰───┴───╯
```

BTY, after this pr, the following commands are impossible either, it's
important to make sure that the implementation doesn't introduce too
much costs:
```nushell
❯ echo a e> a.txt e> a.txt
Error:   × Can't make stderr redirection twice
   ╭─[entry nushell#1:1:1]
 1 │ echo a e> a.txt e> a.txt
   ·                 ─┬
   ·                  ╰── try to remove one
   ╰────

❯ echo a o> a.txt o> a.txt
Error:   × Can't make stdout redirection twice
   ╭─[entry nushell#2:1:1]
 1 │ echo a o> a.txt o> a.txt
   ·                 ─┬
   ·                  ╰── try to remove one
   ╰────
```