Function pack_bitstream_numpy 

pub(crate) fn pack_bitstream_numpy<'py>(
    py: Python<'py>,
    bits: PyReadonlyArray1<'py, u8>,
) -> PyResult<Bound<'py, PyArray1<u64>>>

Pack a 1-D numpy uint8 array into packed u64 words, returning a numpy array. Zero-copy input, single-allocation output.