Add 'number' command for enumeration (#7871)

# Description

This adds a `number` command that will enumerate the input, and add an
`index` and `item` record for each item. The `index` is the number of
the item in the input stream, and `item` is the original value of the
item.

```
> ls | number | get 14
╭───────┬────────────────────────────╮
│ index │ 14                         │
│       │ ╭──────────┬─────────────╮ │
│ item  │ │ name     │ crates      │ │
│       │ │ type     │ dir         │ │
│       │ │ size     │ 832 B       │ │
│       │ │ modified │ 2 weeks ago │ │
│       │ ╰──────────┴─────────────╯ │
╰───────┴────────────────────────────╯
```

# User-Facing Changes

This adds a `number` command.

# 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.

crates/nu-cli/tests/completions.rs

@@ -822,7 +822,7 @@ fn alias_offset_bug_7748() {
 
     // Create an alias
     let alias = r#"alias ea = ^$env.EDITOR /tmp/test.s"#;
-    assert!(support::merge_input(alias.as_bytes(), &mut engine, &mut stack, dir.clone()).is_ok());
+    assert!(support::merge_input(alias.as_bytes(), &mut engine, &mut stack, dir).is_ok());
 
     let mut completer = NuCompleter::new(std::sync::Arc::new(engine), stack);
 
@@ -841,7 +841,7 @@ fn alias_offset_bug_7754() {
 
     // Create an alias
     let alias = r#"alias ll = ls -l"#;
-    assert!(support::merge_input(alias.as_bytes(), &mut engine, &mut stack, dir.clone()).is_ok());
+    assert!(support::merge_input(alias.as_bytes(), &mut engine, &mut stack, dir).is_ok());
 
     let mut completer = NuCompleter::new(std::sync::Arc::new(engine), stack);