geoip.ParseConf() extracted from geoip-update into the geoip package so
both cmds can read GeoIP.conf without duplication.
check-ip gains -geoip-conf flag: reads AccountID+LicenseKey, resolves
mmdb paths into data-dir, builds httpcache.Cachers with geoip.NewCacher.
Background runLoop now refreshes both blocklists and GeoIP DBs on each
tick, hot-swapping geoip2.Reader via atomic.Pointer.Swap + old.Close().