Function write_fixed_bytes 

pub fn write_fixed_bytes<const N: usize>(
    buf: &mut [u8],
    offset: usize,
    v: &FixedBytes<N>,
)

Writes a fixed-capacity byte field into a fixed-layout buffer.

The caller must provide a record data buffer large enough for the field offset and encoded size. Generated record builders pass buffers with R::DATA_LEN bytes.