B001 change caused 'unsupported operand type(s) for -: list and set' during a
full consolidated scan: _db_complete_blocklist returned split_cidr_versions()
output, which is tuple[list, list], but write_blocklist_report()/blocklist_delta()
expect set operands. Return set(v4), set(v6) to match cumulative_blocklist's
contract. Reproduced the exact report path with a populated ledger and
verified it no longer crashes.