Fixes API drift (Init/Sync no longer take a force arg) and adds the
recommended sync/dataset pattern alongside the manual atomic.Pointer
fallbacks for both gitshallow and httpcache.
New package for matching IPs against cohort lists (single IPs and
networks, in separate files or combined) with inbound/outbound/whitelist
semantics. Supports the bitwire-it/ipblocklist data shape out of the box
and is meant to be paired with gitshallow or httpcache for periodic
refresh. Includes README, ipcohort-contains CLI, and tests.
