Move Value to helpers, separate span call (#10121)

# Description

As part of the refactor to split spans off of Value, this moves to using
helper functions to create values, and using `.span()` instead of
matching span out of Value directly.

Hoping to get a few more helping hands to finish this, as there are a
lot of commands to update :)

# User-Facing Changes
<!-- List of all changes that impact the user experience here. This
helps us keep track of breaking changes. -->

# 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` to
check that you're using the standard code style
- `cargo test --workspace` to check that all tests pass (on Windows make
sure to [enable developer
mode](https://learn.microsoft.com/en-us/windows/apps/get-started/developer-mode-features-and-debugging))
- `cargo run -- -c "use std testing; testing run-tests --path
crates/nu-std"` to run the tests for the standard library

> **Note**
> from `nushell` you can also use the `toolkit` as follows
> ```bash
> use toolkit.nu # or use an `env_change` hook to activate it
automatically
> toolkit check pr
> ```
-->

# 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>
Co-authored-by: WindSoilder <windsoilder@outlook.com>

crates/nu-command/src/system/run_external.rs

@@ -506,10 +506,10 @@ impl ExternalCommand {
                                             "{cause}: oops, process '{commandname}' core dumped"
                                         ))
                                     );
-                                    let _ = exit_code_tx.send(Value::Error {
-                                        error: Box::new(ShellError::ExternalCommand { label: "core dumped".to_string(), help: format!("{cause}: child process '{commandname}' core dumped"), span: head }),
-                                        span: head,
-                                    });
+                                    let _ = exit_code_tx.send(Value::error (
+                                        ShellError::ExternalCommand { label: "core dumped".to_string(), help: format!("{cause}: child process '{commandname}' core dumped"), span: head },
+                                        head,
+                                    ));
                                     return Ok(());
                                 }
                             }