This adds the FSChaCha20 stream cipher as specified in BIP324, a
wrapper around the ChaCha20 stream cipher (specified in RFC8439
section 2.4) which automatically rekeys every N messages, and
manages the nonces used for encryption.
Co-authored-by: dhruv <856960+dhruv@users.noreply.github.com>
This is a partial backport of core#28008
https://github.com/bitcoin/bitcoin/pull/28008/commits/0fee267792eb8cbdd48ad78f1712420b5d8d905b
Depends on D19018