feat: apply the --numbered option to acc in reduce command.

[jaeheonji]

Description

The idea for this PR comes from the commands::reduce::reduce_numbered_example test in #4314.

I was curious about the --numbered option of reduce after seeing the following tests:

// FIXME: jt: needs more work
#[ignore]
#[test]
fn reduce_numbered_example() {
    let actual = nu!(
        cwd: ".", pipeline(
        r#"
        echo one longest three bar
        | reduce -n { |it, acc| if ($it.item | str length) > ($acc | str length) {echo $it.item} else {echo $acc}}
        | get index
        "#
        )
    );

    assert_eq!(actual.out, "1");
}

One of the reasons this test cannot work is that the types returned by it and acc are different.
Currently, the -n option converts only the it argument to a block containing an index.

This is why, in other examples, the item property is accessed only in the it.
It is a little bit different to the regular reduce provided in other languages.

So I modified the -n option to apply to both acc and it.

In this case, the test will get the result we expect if we change it like this:

> echo one longest three bar | reduce -n { |it, acc| if ($it.item | str length) > ($acc.item | str length) { echo $it } else { echo $acc } }
╭───────┬─────────╮
│ index │ 1       │
│ item  │ longest │
╰───────┴─────────╯
> 〉echo one longest three bar | reduce -n { |it, acc| if ($it.item | str length) > ($acc.item | str length) { echo $it } else { echo $acc } } | get index
1

Of course, this is a proposal. So, the related tests and examples have not been updated yet.
If we can come to an agreement on this, I will update the rest of the content, including the tests.

Tests

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 --features=extra -- -D warnings -D clippy::unwrap_used -A clippy::needless_collect to check that you're using the standard code style
• cargo test --workspace --features=extra to check that all the tests pass

[fdncred]

I like the proposal

[jaeheonji]

I updated it. If possible, please review it 😸

[fdncred]

lgtm, thanks.