Use static random fill for a fresh array inside a closed provider block

Replace a parameterless BCL RNGCryptoServiceProvider using block starting with one fresh byte[] local and a sole GetBytes(byte[]) call with an ordinary block and RandomNumberGenerator.Fill. Retain the allocation and following consumers/setters. Require one provider reference; skip unknown/shared buffers, other factories/providers, nonzero/ranged/multiple calls, comments, captures/ref/unsafe/async and conditional snapshots. Opt-in modern API port; no algorithm, key-size, seed or ownership policy change.