uniq and uniq-by optimization (#7477) (#7534)

# Description

Refactored the quadratic complexity on `uniq` to use a HashMap, as key I
converted the Value to string.
I tried to use the HashableValue, but it looks it is not very developed
yet and it was getting more complex and difficult.

This improves performance on large data sets.

Fixes https://github.com/nushell/nushell/issues/7477


# Tests + Formatting
```
> let data = fetch "https://home.treasury.gov/system/files/276/yield-curve-rates-1990-2021.csv"
> $data | uniq
```

it keeps original attribute order in Records:
```
> [ {b:2, a:1} {a:1, b:2} ] | uniq 
╭───┬───┬───╮
│ # │ b │ a │
├───┼───┼───┤
│ 0 │ 2 │ 1 │
╰───┴───┴───╯
```

crates/nu-command/src/formats/to/mod.rs

@@ -19,6 +19,7 @@ pub use command::To;
 pub use html::ToHtml;
 pub use json::ToJson;
 pub use md::ToMd;
+pub use nuon::value_to_string;
 pub use nuon::ToNuon;
 pub use text::ToText;
 pub use tsv::ToTsv;

crates/nu-command/src/formats/to/nuon.rs

@@ -50,7 +50,7 @@ impl Command for ToNuon {
     }
 }
 
-fn value_to_string(v: &Value, span: Span) -> Result<String, ShellError> {
+pub fn value_to_string(v: &Value, span: Span) -> Result<String, ShellError> {
     match v {
         Value::Binary { val, .. } => {
             let mut s = String::with_capacity(2 * val.len());