An instance of Aead.
This provides all APIs that start with crypto_aead_xchacha20poly1305_ietf.
crypto_aead_xchacha20poly1305_ietf
See https://libsodium.gitbook.io/doc/secret-key_cryptography/aead/chacha20-poly1305/xchacha20-poly1305_construction
Aead get aeadXChaCha20Poly1305IETF;