Generate XChaCha20 stream for the given 32-byte key and 12-byte
nonce (last 8 bytes of 24 byte nonce prefixed with 4 zero bytes)
and write it into dst and return it.
Nonces MUST be generated using an CSPRNG to generate a sufficiently
random nonce such that a collision is highly unlikely to occur.
Generate XChaCha20 stream for the given 32-byte key and 12-byte nonce (last 8 bytes of 24 byte nonce prefixed with 4 zero bytes) and write it into dst and return it.
Nonces MUST be generated using an CSPRNG to generate a sufficiently random nonce such that a collision is highly unlikely to occur.
stream is like streamXOR with all-zero src.