Use the default RNG factory inside an existing using block

Replace parameterless RNGCryptoServiceProvider construction in using (var rng = new ...) with RandomNumberGenerator.Create(), retaining the scope and disposal. Require all references to be bound byte-array GetBytes/GetNonZeroBytes calls in the block. Preserve arguments, evaluation and null failures. Skip provider options, escapes, other members, captures, async/iterators and conditional snapshots. Opt-in modern-.NET compatibility port.