Rewrite from feat-formmailer WIP:
- Blacklist is *dataset.View[ipcohort.Cohort] — caller wires dataset group
- http.Handler via ServeHTTP — drop-in for any mux
- SuccessBody/ErrorBody []byte — caller loads files; no file I/O per request
- Rate limiter per-instance (sync.Once init), not global
- Fields configurable (default standard names, not GravityForms input_N)
- AllowedCountries []string for geo-blocking via iploc (nil = allow all)
- ContainsAddr used directly (pre-parsed netip.Addr, no re-parse)
- No Init()/Run() — caller drives dataset lifecycle
- Fix getErrorBotty typo; expose support email only to legitimate errors
httpcache.Cacher gains:
- Username/Password: Basic Auth, stripped before following redirects
- MaxAge: skip HTTP if local file mtime is within this duration
- MinInterval: skip HTTP if last Fetch attempt was within this duration
- Transform: post-process response body (e.g. extract .mmdb from tar.gz)
geoip.Downloader now builds an httpcache.Cacher via NewCacher(), removing
its own HTTP client. ExtractMMDB is now exported for use as a Transform.
check-ip-blacklist renamed to check-ip; adds -city-db / -asn-db flags
for GeoLite2 lookup (country, city, subdivision, ASN) printed after each
blocklist result.
