Function multi_probe_keys 

pub fn multi_probe_keys(
    base_hash: u64,
    margins: &[(usize, f32)],
    num_probes: usize,
) -> Vec<u64>

Generate multi-probe hash keys by flipping the most uncertain bits.

Given the base hash and margin info (sorted ascending by uncertainty), produces the base key plus num_probes perturbed keys.