Benchmark each pipeline element (#7854)

# Description

Adds a `profile` command that profiles each pipeline element of a block
and can also recursively step into child blocks.

# Limitations
* It is implemented using pipeline metadata which currently get lost in
some circumstances (e.g.,
https://github.com/nushell/nushell/issues/4501). This means that the
profiler will lose data coming from subexpressions. This issue will
hopefully be solved in the future.
* It also does not step into individual loop iteration which I'm not
sure why but maybe that's a good thing.

# User-Facing Changes

Shouldn't change any existing behavior.

# Tests + Formatting

Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect` to check that you're using the standard code
style
- `cargo test --workspace` to check that all tests pass

# After Submitting

If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.

---------

Co-authored-by: Darren Schroeder <343840+fdncred@users.noreply.github.com>

crates/nu-command/src/filesystem/ls.rs

@@ -264,9 +264,9 @@ impl Command for Ls {
                 _ => Some(Value::Nothing { span: call_span }),
             })
             .into_pipeline_data_with_metadata(
-                PipelineMetadata {
+                Box::new(PipelineMetadata {
                     data_source: DataSource::Ls,
-                },
+                }),
                 engine_state.ctrlc.clone(),
             ))
     }