Function read_u64_le 

pub fn read_u64_le(bytes: &[u8]) -> u64

Read up to 8 bytes as a little-endian u64, zero-padding the high bytes when fewer than 8 bytes are supplied.

This preserves Vortex’s least-significant-bit-first bitmap numbering on little- and big-endian targets. For a full 8-byte slice it lowers to a single word load.