Function encrypt_file_buffer_with_send_key 

fn encrypt_file_buffer_with_send_key(
    key_store: &KeyStore<KeySlotIds>,
    wrapped_send_key: &str,
    buffer: &[u8],
) -> Result<Vec<u8>, CryptoError>

Encrypt buffer under the send key wrapped in wrapped_send_key (the key field of a [bitwarden_api_api::models::SendRequestModel], which is the send key encrypted under the user key). Mirrors SendClient::encrypt_buffer, but sources the key from the just-built create request instead of a round-tripped Send, so the create request can carry the true ciphertext length before the send exists on the server.