Remove a few unsafe bits in S.P.Uri, S.N.Ping, System.Transactions.Local

[EgorBo]

diffs (size regression in ParseCanonicalName is due to inlining of Parse)

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[Copilot]

Pull Request Overview

This PR removes several unsafe code paths across three libraries by adopting safer constructs and modern C# features.

• Replace fixed buffers in Xactopt marshalling with InlineArray and safe spans
• Refactor IPv4AddressHelper.ParseCanonicalName to eliminate pointer math and use spans
• Remove unsafe methods in Ping.RawSocket, replacing pointer-based socket options with spans

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
System/Transactions/DtcProxyShim/Xactopt.cs	Switched from unsafe fixed byte buffer to InlineArray, removed unsafe from marshaller methods
System.Private.Uri/src/System/UriExt.cs	Dropped unused unsafe modifier from GetRelativeSerializationString
System.Private.Uri/src/System/IPv4AddressHelper.cs	Rewrote ParseCanonicalName to use spans instead of stackalloc pointers and removed obsolete Parse
System.Net.Ping/src/System/Net/NetworkInformation/Ping.RawSocket.cs	Removed unsafe contexts in raw socket setup and replaced pointer options with ReadOnlySpan<byte>

Comments suppressed due to low confidence (2)

src/libraries/System.Net.Ping/src/System/Net/NetworkInformation/Ping.RawSocket.cs:109

• [nitpick] The variable name opt is ambiguous. Consider a more descriptive name like recvErrOptionValue or optionBytes to clarify its purpose.

ReadOnlySpan<byte> opt = BitConverter.IsLittleEndian ? [1, 0, 0, 0] : [0, 0, 0, 1];

src/libraries/System.Private.Uri/src/System/IPv4AddressHelper.cs:30

• This array literal creates a heap-allocated array before converting to a Span. For a small fixed-size buffer, consider using stackalloc, e.g.: Span<byte> numbers = stackalloc byte[NumberOfLabels] { ... }; to avoid heap allocations.

Span<byte> numbers =

[EgorBo]

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