What parseCidr returns and what stringifyCidr accepts: a
ParsedCidrv4 or a ParsedCidrv6, the block in the dialect
it was written in plus an optional zone ID. Assignable to Cidr,
so a parse result goes straight into every cidr* operation; none of
them reads the zone.
Usage
import { type ParsedCidr } from "mod.ts";