Function encode 

pub fn encode(
    params: &LnavParams,
    opts: &LnavOptions,
) -> Result<[Vec<u8>; 3], LnavError>

Encodes clock and ephemeris parameters into LNAV subframes 1-3.

Returns the three 300-bit subframes (most significant first) keyed 1/2/3. Out-of-range parameters yield LnavError::OutOfRange.