Extract the file/git/httpcache mode switch into newSource and the Group
wiring into newBlocklists. main becomes flag parsing + exit code logic
only; run owns ctx and the check. Helpers (loadCohort, cacheDir,
splitCSV, loadWhitelist) are small and single-purpose.
Still exercises dataset.Group + background refresh, gitshallow, and
httpcache as before.
- Each package gets its own go.mod: net/{dataset,httpcache,gitshallow,ipcohort,geoip,formmailer}
- go.work with replace directives for cross-module workspace resolution
- dataset.Syncer/NopSyncer moved here from httpcache; callers duck-type it
- dataset.View[T] returned by Add to prevent Init/Sync/Run misuse on group members
- cmd/check-ip moved from net/ipcohort/cmd/check-ip to top-level cmd/check-ip
- Add net/ipcohort/cmd/ipcohort-contains for standalone cohort membership testing
