Fix to nuon --serialize of closure (#15357)

# Description
Closes #15351

Adds quotes that were missed in #14698 with the proper escaping.


# User-Facing Changes
`to nuon --serialize` will now produce a quoted string instead of
illegal nuon when given a closure

# Tests + Formatting
Reenable the `to nuon` rejection of closures in the base state test.
Added test for quoting.

crates/nuon/src/to.rs

@@ -99,7 +99,9 @@ fn value_to_string(
         }
         Value::Closure { val, .. } => {
             if serialize_types {
-                Ok(val.coerce_into_string(engine_state, span)?.to_string())
+                Ok(escape_quote_string(
+                    &val.coerce_into_string(engine_state, span)?,
+                ))
             } else {
                 Err(ShellError::UnsupportedInput {
                     msg: "closures are currently not deserializable (use --serialize to serialize as a string)".into(),