Function encrypt_file_to 

pub fn encrypt_file_to(
    src: &Path,
    dst: &Path,
    derived_key: &[u8; 32],
    salt: [u8; 16],
    file_id: Option<[u8; 16]>,
    zstd: Option<u8>,
) -> Result<Option<FileHeader>>

Encrypt src into dst.