feat: store packet- and byte-weighted MAAD measures#112

feat(netflow-db): add --maad-workers pipeline option

fix(netflow-db): verify MAAD measure presence per scope key

fix(netflow-db): drop and log zero-packet flows before aggregation

fix(netflow-db): surface later-batch errors only after the current batch publishes

perf(netflow-db): decode the next nfcapd batch while publishing the current one

perf(netflow-db): compute a scope's MAAD measures together and in parallel

feat(web): choose the MAAD measure on file details

feat(netflow-db): store packet- and byte-weighted MAAD measures