REFACTOR: format some example commands (#8223)

hellord 👋 😋 

# Description
this PR fixes the format of a few single-line examples and the
indentation of some multi-line examples
- single-line example formatting
  - `compact`
- multi-line example indentation
  - `update cells`
  - `error make
  - `split-by`

# User-Facing Changes
- `compact`

from
```bash
Examples:
  Filter out all records where 'Hello' is null (returns nothing)
  > [["Hello" "World"]; [null 3]]| compact Hello

  Filter out all records where 'World' is null (Returns the table)
  > [["Hello" "World"]; [null 3]]| compact World
```
to
```bash
Examples:
  Filter out all records where 'Hello' is null (returns nothing)
  > [["Hello" "World"]; [null 3]] | compact Hello

  Filter out all records where 'World' is null (Returns the table)
  > [["Hello" "World"]; [null 3]] | compact World
```
- `update cells`

from
```bash
Examples:
  Update the zero value cells to empty strings.
  > [
    ["2021-04-16", "2021-06-10", "2021-09-18", "2021-10-15", "2021-11-16", "2021-11-17", "2021-11-18"];
    [          37,            0,            0,            0,           37,            0,            0]
] | update cells { |value|
      if $value == 0 {
        ""
      } else {
        $value
      }
}

  Update the zero value cells to empty strings in 2 last columns.
  > [
    ["2021-04-16", "2021-06-10", "2021-09-18", "2021-10-15", "2021-11-16", "2021-11-17", "2021-11-18"];
    [          37,            0,            0,            0,           37,            0,            0]
] | update cells -c ["2021-11-18", "2021-11-17"] { |value|
        if $value == 0 {
          ""
        } else {
          $value
        }
}
```
to
```bash
Examples:
  Update the zero value cells to empty strings.
  > [
        ["2021-04-16", "2021-06-10", "2021-09-18", "2021-10-15", "2021-11-16", "2021-11-17", "2021-11-18"];
        [          37,            0,            0,            0,           37,            0,            0]
    ] | update cells { |value|
          if $value == 0 {
            ""
          } else {
            $value
          }
    }

  Update the zero value cells to empty strings in 2 last columns.
  > [
        ["2021-04-16", "2021-06-10", "2021-09-18", "2021-10-15", "2021-11-16", "2021-11-17", "2021-11-18"];
        [          37,            0,            0,            0,           37,            0,            0]
    ] | update cells -c ["2021-11-18", "2021-11-17"] { |value|
            if $value == 0 {
              ""
            } else {
              $value
            }
    }
```
- `split-by`

from
```bash
Examples:
  split items by column named "lang"
  >
                {
                    '2019': [
                      { name: 'andres', lang: 'rb', year: '2019' },
                      { name: 'jt', lang: 'rs', year: '2019' }
                    ],
                    '2021': [
                      { name: 'storm', lang: 'rs', 'year': '2021' }
                    ]
                } | split-by lang
```
to
```bash
Examples:
  split items by column named "lang"
  > {
        '2019': [
          { name: 'andres', lang: 'rb', year: '2019' },
          { name: 'jt', lang: 'rs', year: '2019' }
        ],
        '2021': [
          { name: 'storm', lang: 'rs', 'year': '2021' }
        ]
    } | split-by lang
```
- `error make`

from
```bash
Examples:
  Create a custom error for a custom command
  > def foo [x] {
      let span = (metadata $x).span;
      error make {msg: "this is fishy", label: {text: "fish right here", start: $span.start, end: $span.end } }
    }

  Create a simple custom error for a custom command
  > def foo [x] {
      error make {msg: "this is fishy"}
    }
```
to
```bash
Examples:
  Create a custom error for a custom command
  > def foo [x] {
        let span = (metadata $x).span;
        error make {msg: "this is fishy", label: {text: "fish right here", start: $span.start, end: $span.end } }
    }

  Create a simple custom error for a custom command
  > def foo [x] {
        error make {msg: "this is fishy"}
    }
```

# Tests + Formatting
no tests have been changed => this is a pure formatting PR

- ✔️ `cargo fmt --all`
- ✔️ `cargo clippy --workspace -- -D warnings -D
clippy::unwrap_used -A clippy::needless_collect`
- ✔️ `cargo test --workspace`

# After Submitting
need to change the book? 🤔

crates/nu-command/src/filters/split_by.rs

@@ -37,8 +37,7 @@ impl Command for SplitBy {
     fn examples(&self) -> Vec<Example> {
         vec![Example {
             description: "split items by column named \"lang\"",
-            example: r#"
+            example: r#"{
-                {
         '2019': [
           { name: 'andres', lang: 'rb', year: '2019' },
           { name: 'jt', lang: 'rs', year: '2019' }
@@ -46,8 +45,7 @@ impl Command for SplitBy {
         '2021': [
           { name: 'storm', lang: 'rs', 'year': '2021' }
         ]
-                } | split-by lang
+    } | split-by lang"#,
-                "#,
             result: Some(Value::Record {
                 cols: vec!["rb".to_string(), "rs".to_string()],
                 vals: vec![