feat(netflow-db): add measure-weighted MAAD estimator#111

fix(netflow-db): keep weighted MAAD finite and scale-invariant at extreme weights

fix(netflow-db): skip unused MAAD work and check weights against a reference

perf(netflow-db): raise only distinct weighted masses and spread q values across threads

perf(netflow-db): share one prefix-level walk across MAAD measures

feat(netflow-db): add measure-weighted MAAD estimator