json2: pass-along policy in ArrayParser, remove_cv_t and decay to remove const / volatile when calling to_json so we don't need Parser<const T> when we have Parser<T>

json2: more tests; less output in case of error; benchmark;  cano::from_String: using from_chars where available

json2: parse all arithmeitc types; require string_view to be empty in non-consuming parse call; some bugfixes