Function write_header 

pub fn write_header(
    data: &mut [u8],
    discriminator: u8,
    version: u8,
    flags: u8,
) -> Result<(), ProgramError>

Write the standard 8-byte Jiminy account header.

Sets the discriminator, version, and flags. Reserved byte and data_len are zeroed. Call this immediately after allocating the account (and after zero_init if desired).

let mut raw = account.try_borrow_mut()?;
jiminy::write_header(&mut raw, VAULT_DISC, 1, 0)?;
let mut w = DataWriter::new(&mut raw[HEADER_LEN..]);
w.write_u64(0)?;              // balance
w.write_address(&authority)?;  // authority pubkey