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-cli/src/eval_file.rs

@@ -96,7 +96,7 @@ pub fn evaluate_file(
     engine_state.merge_delta(working_set.delta)?;
 
     // Check if the file contains a main command.
-    if engine_state.find_decl(b"main", &[]).is_some() {
+    let exit_code = if engine_state.find_decl(b"main", &[]).is_some() {
         // Evaluate the file, but don't run main yet.
         let pipeline =
             match eval_block::<WithoutDebug>(engine_state, stack, &block, PipelineData::empty()) {
@@ -109,26 +109,29 @@ pub fn evaluate_file(
             };
 
         // Print the pipeline output of the last command of the file.
-        let exit_code = pipeline.print(engine_state, stack, true, false)?;
-        if exit_code != 0 {
-            std::process::exit(exit_code as i32);
+        if let Some(status) = pipeline.print(engine_state, stack, true, false)? {
+            if status.code() != 0 {
+                std::process::exit(status.code())
+            }
         }
 
         // Invoke the main command with arguments.
         // Arguments with whitespaces are quoted, thus can be safely concatenated by whitespace.
         let args = format!("main {}", args.join(" "));
-        if !eval_source(
+        eval_source(
             engine_state,
             stack,
             args.as_bytes(),
             "<commandline>",
             input,
             true,
-        ) {
-            std::process::exit(1);
-        }
-    } else if !eval_source(engine_state, stack, &file, file_path_str, input, true) {
-        std::process::exit(1);
+        )
+    } else {
+        eval_source(engine_state, stack, &file, file_path_str, input, true)
+    };
+
+    if exit_code != 0 {
+        std::process::exit(exit_code)
     }
 
     info!("evaluate {}:{}:{}", file!(), line!(), column!());