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_plugin_example/src/commands/collect_bytes.rs

@@ -1,22 +1,22 @@
 use nu_plugin::{EngineInterface, EvaluatedCall, PluginCommand};
 use nu_protocol::{
-    Category, Example, LabeledError, PipelineData, RawStream, Signature, Type, Value,
+    ByteStream, Category, Example, LabeledError, PipelineData, Signature, Type, Value,
 };
 
 use crate::ExamplePlugin;
 
-/// `<list<string>> | example collect-external`
-pub struct CollectExternal;
+/// `<list<string>> | example collect-bytes`
+pub struct CollectBytes;
 
-impl PluginCommand for CollectExternal {
+impl PluginCommand for CollectBytes {
     type Plugin = ExamplePlugin;
 
     fn name(&self) -> &str {
-        "example collect-external"
+        "example collect-bytes"
     }
 
     fn usage(&self) -> &str {
-        "Example transformer to raw external stream"
+        "Example transformer to byte stream"
     }
 
     fn search_terms(&self) -> Vec<&str> {
@@ -34,7 +34,7 @@ impl PluginCommand for CollectExternal {
 
     fn examples(&self) -> Vec<Example> {
         vec![Example {
-            example: "[a b] | example collect-external",
+            example: "[a b] | example collect-bytes",
             description: "collect strings into one stream",
             result: Some(Value::test_string("ab")),
         }]
@@ -47,26 +47,19 @@ impl PluginCommand for CollectExternal {
         call: &EvaluatedCall,
         input: PipelineData,
     ) -> Result<PipelineData, LabeledError> {
-        let stream = input.into_iter().map(|value| {
-            value
-                .as_str()
-                .map(|str| str.as_bytes())
-                .or_else(|_| value.as_binary())
-                .map(|bin| bin.to_vec())
-        });
-        Ok(PipelineData::ExternalStream {
-            stdout: Some(RawStream::new(Box::new(stream), None, call.head, None)),
-            stderr: None,
-            exit_code: None,
-            span: call.head,
-            metadata: None,
-            trim_end_newline: false,
-        })
+        Ok(PipelineData::ByteStream(
+            ByteStream::from_result_iter(
+                input.into_iter().map(Value::coerce_into_binary),
+                call.head,
+                None,
+            ),
+            None,
+        ))
     }
 }
 
 #[test]
 fn test_examples() -> Result<(), nu_protocol::ShellError> {
     use nu_plugin_test_support::PluginTest;
-    PluginTest::new("example", ExamplePlugin.into())?.test_command_examples(&CollectExternal)
+    PluginTest::new("example", ExamplePlugin.into())?.test_command_examples(&CollectBytes)
 }

crates/nu_plugin_example/src/commands/mod.rs

@@ -24,14 +24,14 @@ pub use env::Env;
 pub use view_span::ViewSpan;
 
 // Stream demos
-mod collect_external;
+mod collect_bytes;
 mod echo;
 mod for_each;
 mod generate;
 mod seq;
 mod sum;
 
-pub use collect_external::CollectExternal;
+pub use collect_bytes::CollectBytes;
 pub use echo::Echo;
 pub use for_each::ForEach;
 pub use generate::Generate;

crates/nu_plugin_example/src/lib.rs

@@ -24,7 +24,7 @@ impl Plugin for ExamplePlugin {
             Box::new(ViewSpan),
             Box::new(DisableGc),
             // Stream demos
-            Box::new(CollectExternal),
+            Box::new(CollectBytes),
             Box::new(Echo),
             Box::new(ForEach),
             Box::new(Generate),