[NET] IPNetwork clears the lower bits instead of throwing.

[ManickaP]

Fixes #117114

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[Copilot]

Pull Request Overview

This PR changes the IPNetwork implementation to automatically clear bits outside the network prefix instead of throwing an exception, and updates tests to verify the new behavior.

• IPNetwork constructor and TryParse now use ClearNonZeroBitsAfterNetworkPrefix to trim bits rather than rejecting the input.
• The obsolete HasNonZeroBitsAfterNetworkPrefix logic and related error resource were removed.
• Tests were updated to compute expected base addresses, moved previously invalid cases into valid data, and corrected a typo in prefixLength.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/libraries/System.Net.Primitives/tests/FunctionalTests/IPNetworkTest.cs	Updated valid/invalid data, added helper methods to calculate expected base addresses
src/libraries/System.Net.Primitives/src/System/Net/IPNetwork.cs	Replaced non-zero-bit check with clearing logic, simplified TryParse
src/libraries/System.Net.Primitives/src/Resources/Strings.resx	Removed obsolete error message for invalid base addresses

Comments suppressed due to low confidence (3)

src/libraries/System.Net.Primitives/tests/FunctionalTests/IPNetworkTest.cs:39

• Add a test case for the IPv6 /0 network (e.g. { "::/0" }) to ensure the new zero-prefix branch for IPv6 is covered.

            { "192.168.0.10/0" },

src/libraries/System.Net.Primitives/src/System/Net/IPNetwork.cs:240

• [nitpick] Consider renaming ClearNonZeroBitsAfterNetworkPrefix to something like ComputeNetworkAddress or TrimToNetworkPrefix to better reflect that this method returns the trimmed base address.

        private static IPAddress ClearNonZeroBitsAfterNetworkPrefix(IPAddress baseAddress, int prefixLength)

src/libraries/System.Net.Primitives/src/System/Net/IPNetwork.cs:261

• [nitpick] This comment is a bit unclear—consider clarifying or removing it, since the reasoning about shift width may not be obvious to future readers.

                // Bitwise shift works only for lower 7-bits count operands.

[skyoxZ]

The baseAddress is the original non-mask address. Is it intended?

[ManickaP]

Fudge, good catch. It also means we don't have a good test coverage for this. I'll put up a PR asap.