add from ndnuon and to ndnuon to stdlib (#14334)

# Description
i was playing with the NDNUON format and using local definitions of
`from ndnuon` and `to ndnuon` but then i thought they could live in the
standard library next to `from ndjson` and `to ndjson` 😋

# User-Facing Changes
users can now add the following to their configs and get NDNUON ready to
go
```nushell
use std formats ["from ndnuon" "to ndnuon"]
```

# Tests + Formatting
i did simply mimic the tests for `from ndjson` and `to ndjson`, i hope
it's fine since the recent big change to the standard library

# After Submitting

---------

Co-authored-by: Douglas <32344964+NotTheDr01ds@users.noreply.github.com>

crates/nu-std/std/formats/mod.nu

@@ -28,3 +28,13 @@ export def "to ndjson" []: any -> string {
 export def "to jsonl" []: any -> string {
     each { to json --raw } | to text
 }
+
+# Convert from NDNUON (newline-delimited NUON), to structured data
+export def "from ndnuon" []: [string -> any] {
+    lines | each { from nuon }
+}
+
+# Convert structured data to NDNUON, i.e. newline-delimited NUON
+export def "to ndnuon" []: [any -> string] {
+    each { to nuon --raw } | to text
+}