don't use table compaction in to nuon if not a table (#4671)

* don't use table compaction in to nuon if not a table

* Make a proper nuon conversion test

* more nuon tests

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

@@ -5,6 +5,7 @@ mod html;
 mod ics;
 mod json;
 mod markdown;
+mod nuon;
 mod ods;
 mod sqlite;
 mod ssv;