add "to nuon" enumeration of possible styles (#12591)

# Description
in order to change the style of the _serialized_ NUON data,
`nuon::to_nuon` takes three mutually exclusive arguments, `raw: bool`,
`tabs: Option<usize>` and `indent: Option<usize>` 🤔
this begs to use an enumeration with all possible alternatives, right?

this PR changes the signature of `nuon::to_nuon` to use `nuon::ToStyle`
which has three variants
- `Raw`: no newlines
- `Tabs(n: usize)`: newlines and `n` tabulations as indent
- `Spaces(n: usize)`: newlines and `n` spaces as indent

# User-Facing Changes
the signature of `nuon::to_nuon` changes from
```rust
to_nuon(
    input: &Value,
    raw: bool,
    tabs: Option<usize>,
    indent: Option<usize>,
    span: Option<Span>,
) -> Result<String, ShellError>
```
to
```rust
to_nuon(
    input: &Value,
    style: ToStyle,
    span: Option<Span>
) -> Result<String, ShellError>
```

# Tests + Formatting

# After Submitting

crates/nu-command/tests/commands/database/into_sqlite.rs

@@ -330,7 +330,7 @@ fn into_sqlite_big_insert() {
                 )
                 .unwrap();
 
-            let nuon = nuon::to_nuon(&value, true, None, None, Some(Span::unknown())).unwrap()
+            let nuon = nuon::to_nuon(&value, nuon::ToStyle::Raw, Some(Span::unknown())).unwrap()
                 + &line_ending();
 
             nuon_file.write_all(nuon.as_bytes()).unwrap();