preserve space by letting to nuon only add quotes when necessary (#6379)

* preserve space by letting `to nuon` only add quotes when necessary

* fix CI, add quotes with colon

* fmt

* add more chars to blacklist

crates/nu-command/tests/format_conversions/nuon.rs

@@ -249,3 +249,21 @@ fn to_nuon_converts_columns_with_spaces() {
     ));
     assert!(actual.err.is_empty());
 }
+
+#[test]
+fn to_nuon_does_not_quote_unnecessarily() {
+    let actual = nu!(
+        cwd: "tests/fixtures/formats", pipeline(
+            r#"
+        let test = [["a", "b", "c d"]; [1 2 3] [4 5 6]]; $test | to nuon
+    "#
+    ));
+    assert_eq!(actual.out, "[[a, b, \"c d\"]; [1, 2, 3], [4, 5, 6]]");
+    let actual = nu!(
+        cwd: "tests/fixtures/formats", pipeline(
+            r#"
+         let a = {"ro name": "sam" rank: 10}; $a | to nuon
+    "#
+    ));
+    assert_eq!(actual.out, "{\"ro name\": sam, rank: 10}");
+}