Function tac_bytes 

pub fn tac_bytes(
    data: &[u8],
    separator: u8,
    before: bool,
    out: &mut impl Write,
) -> Result<()>

Reverse records separated by a single byte. Uses backward SIMD scan (memrchr_iter) to process records from back to front, building batched IoSlice references for zero-copy writev output. O(IOV_BATCH) memory — no positions Vec allocation needed at all. For 100MB/2.5M lines: saves ~20MB positions Vec + ~40MB IoSlice Vec.