`proptest` caught a failing test condition for `&&` as a literal string. It requires a quotation to be parsed correctly by current `from nuon`
https://github.com/nushell/nushell/actions/runs/3753242377/jobs/6376308675
The change in the parser that now returns an error was introduced by https://github.com/nushell/nushell/pull/7241
This in theory doesn't have to be an error (it is a diagnostic for nushell code) but it is probably better safe than sorry to require quotation here.
- Add a test for `&&` in `to nuon` from proptest fail
- Fix `to nuon` generating invalid `&&` literal
- Add a test for `,` in `to nuon`/`from nuon` cycle
- Bonus: should already be properly quoted
* remove unnecessary FlatShape
* add proptest
* remove files that belonged in another PR
* more tests, more chars
* add exception for parser error unrelated ot PR
