IPNetwork.Contains handles IPv4-mapped addresses inconsistently for IPv6 networks

[wfurt]

IPNetwork.Contains uses the queried address to choose between IPv4 and IPv6 comparison logic. When an IPv4-mapped IPv6 address is queried against an IPv6 network, it can incorrectly use the IPv4 comparison path.

Expected behavior:

IPv4 networks continue to accept equivalent IPv4-mapped addresses.
IPv6 networks use IPv6 prefix semantics for all IPv6 addresses, including IPv4-mapped addresses.
Example:

IPNetwork network = IPNetwork.Parse("2a00::/13");
IPAddress address = IPAddress.Parse("::ffff:42.42.42.42");

Console.WriteLine(network.Contains(address));

The comparison path should be selected from the network’s address family rather than solely from the queried address.

[dotnet-policy-service]

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