Npgsql 9 added support for mapping PG cidr to .NET IPNetwork (see #5821). Since Npgsql 9 still targeted .NET 6 - where IPNetwork wasn't yet introduced - we did not make this the default.

As .NET 6 is now out of support and no longer targeted by Npgsql 10, we should make the breaking change and switch this mapping to be the default for cidr. Also obsolete NpgsqlCidr.