Replace ExternalStream with new ByteStream type (#12774)

# Description
This PR introduces a `ByteStream` type which is a `Read`-able stream of
bytes. Internally, it has an enum over three different byte stream
sources:
```rust
pub enum ByteStreamSource {
    Read(Box<dyn Read + Send + 'static>),
    File(File),
    Child(ChildProcess),
}
```

This is in comparison to the current `RawStream` type, which is an
`Iterator<Item = Vec<u8>>` and has to allocate for each read chunk.

Currently, `PipelineData::ExternalStream` serves a weird dual role where
it is either external command output or a wrapper around `RawStream`.
`ByteStream` makes this distinction more clear (via `ByteStreamSource`)
and replaces `PipelineData::ExternalStream` in this PR:
```rust
pub enum PipelineData {
    Empty,
    Value(Value, Option<PipelineMetadata>),
    ListStream(ListStream, Option<PipelineMetadata>),
    ByteStream(ByteStream, Option<PipelineMetadata>),
}
```

The PR is relatively large, but a decent amount of it is just repetitive
changes.

This PR fixes #7017, fixes #10763, and fixes #12369.

This PR also improves performance when piping external commands. Nushell
should, in most cases, have competitive pipeline throughput compared to,
e.g., bash.
| Command | Before (MB/s) | After (MB/s) | Bash (MB/s) |
| -------------------------------------------------- | -------------:|
------------:| -----------:|
| `throughput \| rg 'x'` | 3059 | 3744 | 3739 |
| `throughput \| nu --testbin relay o> /dev/null` | 3508 | 8087 | 8136 |

# User-Facing Changes
- This is a breaking change for the plugin communication protocol,
because the `ExternalStreamInfo` was replaced with `ByteStreamInfo`.
Plugins now only have to deal with a single input stream, as opposed to
the previous three streams: stdout, stderr, and exit code.
- The output of `describe` has been changed for external/byte streams.
- Temporary breaking change: `bytes starts-with` no longer works with
byte streams. This is to keep the PR smaller, and `bytes ends-with`
already does not work on byte streams.
- If a process core dumped, then instead of having a `Value::Error` in
the `exit_code` column of the output returned from `complete`, it now is
a `Value::Int` with the negation of the signal number.

# After Submitting
- Update docs and book as necessary
- Release notes (e.g., plugin protocol changes)
- Adapt/convert commands to work with byte streams (high priority is
`str length`, `bytes starts-with`, and maybe `bytes ends-with`).
- Refactor the `tee` code, Devyn has already done some work on this.

---------

Co-authored-by: Devyn Cairns <devyn.cairns@gmail.com>

crates/nu-command/src/debug/inspect.rs

@@ -29,7 +29,7 @@ impl Command for Inspect {
         input: PipelineData,
     ) -> Result<PipelineData, ShellError> {
         let input_metadata = input.metadata();
-        let input_val = input.into_value(call.head);
+        let input_val = input.into_value(call.head)?;
         if input_val.is_nothing() {
             return Err(ShellError::PipelineEmpty {
                 dst_span: call.head,

crates/nu-command/src/debug/timeit.rs

@@ -53,13 +53,12 @@ impl Command for TimeIt {
                 eval_block(engine_state, stack, block, input)?
             } else {
                 let eval_expression_with_input = get_eval_expression_with_input(engine_state);
-                eval_expression_with_input(engine_state, stack, command_to_run, input)
-                    .map(|res| res.0)?
+                eval_expression_with_input(engine_state, stack, command_to_run, input)?.0
             }
         } else {
             PipelineData::empty()
         }
-        .into_value(call.head);
+        .into_value(call.head)?;
 
         let end_time = Instant::now();