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/bytes/starts_with.rs

@@ -60,63 +60,13 @@ impl Command for BytesStartsWith {
             pattern,
             cell_paths,
         };
-
-        match input {
-            PipelineData::ExternalStream {
-                stdout: Some(stream),
-                span,
-                ..
-            } => {
-                let mut i = 0;
-
-                for item in stream {
-                    let byte_slice = match &item {
-                        // String and binary data are valid byte patterns
-                        Ok(Value::String { val, .. }) => val.as_bytes(),
-                        Ok(Value::Binary { val, .. }) => val,
-                        // If any Error value is output, echo it back
-                        Ok(v @ Value::Error { .. }) => return Ok(v.clone().into_pipeline_data()),
-                        // Unsupported data
-                        Ok(other) => {
-                            return Ok(Value::error(
-                                ShellError::OnlySupportsThisInputType {
-                                    exp_input_type: "string and binary".into(),
-                                    wrong_type: other.get_type().to_string(),
-                                    dst_span: span,
-                                    src_span: other.span(),
-                                },
-                                span,
-                            )
-                            .into_pipeline_data());
-                        }
-                        Err(err) => return Err(err.to_owned()),
-                    };
-
-                    let max = byte_slice.len().min(arg.pattern.len() - i);
-
-                    if byte_slice[..max] == arg.pattern[i..i + max] {
-                        i += max;
-
-                        if i >= arg.pattern.len() {
-                            return Ok(Value::bool(true, span).into_pipeline_data());
-                        }
-                    } else {
-                        return Ok(Value::bool(false, span).into_pipeline_data());
-                    }
-                }
-
-                // We reached the end of the stream and never returned,
-                // the pattern wasn't exhausted so it probably doesn't match
-                Ok(Value::bool(false, span).into_pipeline_data())
-            }
-            _ => operate(
-                starts_with,
-                arg,
-                input,
-                call.head,
-                engine_state.ctrlc.clone(),
-            ),
-        }
+        operate(
+            starts_with,
+            arg,
+            input,
+            call.head,
+            engine_state.ctrlc.clone(),
+        )
     }
 
     fn examples(&self) -> Vec<Example> {