Add ArcBuffer support to Orleans serialization

[ReubenBond]

Summary

• Adds ArcBuffer input support for serialization readers, including multi-page reads, position/length tracking, skip, and fork/resume behavior.
• Adds Serializer and Serializer<T> overloads for deserializing directly from ArcBuffer.
• Adds Writer.Create(ArcBufferWriter, ...) via a wrapper which does not dispose the underlying ArcBufferWriter.
• Updates serialization test helpers and adds focused ArcBufferWriter serialization tests for multi-page payloads and serializer round-trips.

Microsoft Reviewers: Open in CodeFlow

[Copilot]

Pull request overview

This PR extends Orleans’ serialization buffer plumbing to support ArcBuffer as an input source for readers and deserializers, enabling multi-page reads and round-trips directly over ArcBuffer/ArcBufferWriter.

Changes:

• Added Reader.Create(ArcBuffer, ...) and an ArcBufferReaderInput adaptor for multi-page reading/positioning/skip/fork behavior.
• Added Serializer/Serializer<T> overloads to deserialize directly from ArcBuffer.
• Added Writer.Create(ArcBufferWriter, ...) using a wrapper which prevents disposing the underlying ArcBufferWriter, plus new unit tests and testkit updates.

Show a summary per file

File	Description
test/Orleans.Serialization.UnitTests/Buffers/ArcBufferWriterSerializationTests.cs	Adds focused tests for multi-page writer/reader and serializer round-trips using ArcBufferWriter + ArcBuffer.
src/Orleans.Serialization/Serializer.cs	Adds Deserialize(... ArcBuffer ...) overloads on Serializer and Serializer<T>.
src/Orleans.Serialization/Buffers/Writer.cs	Adds Writer.Create(ArcBufferWriter, ...) and ArcBufferWriterWrapper to avoid disposing the underlying writer.
src/Orleans.Serialization/Buffers/Reader.cs	Adds Reader.Create(ArcBuffer, ...) and integrates ArcBufferReaderInput into reader fast paths and navigation logic.
src/Orleans.Serialization/Buffers/Adaptors/BufferSliceReaderInput.cs	Introduces ArcBufferReaderInput adaptor implementation.
src/Orleans.Serialization.TestKit/FieldCodecTester.cs	Updates serialization test helper to produce/format/deserialize via ArcBufferWriter + ArcBuffer.

Copilot's findings

Comments suppressed due to low confidence (2)

src/Orleans.Serialization/Serializer.cs:889

• This new public Deserialize(ArcBuffer source) overload (on Serializer<T>) changes the Orleans.Serialization public API surface, but src/api/Orleans.Serialization/Orleans.Serialization.cs does not currently include it. Update the generated API surface file to reflect this addition.

        public T Deserialize(ArcBuffer source)
        {
            using var session = _sessionPool.GetSession();
            var reader = Reader.Create(source, session);
            var field = reader.ReadFieldHeader();
            return _codec.ReadValue(ref reader, field);
        }

src/Orleans.Serialization/Buffers/Adaptors/BufferSliceReaderInput.cs:125

• ArcBufferReaderInput is in the Orleans.Serialization.Buffers.Adaptors namespace, but it references ArcBuffer and ArcBufferPage which are declared in Orleans.Serialization.Buffers. This file does not import that namespace, so these type references will not resolve and the project will fail to compile. Add a using Orleans.Serialization.Buffers; (or fully-qualify the types) so ArcBuffer/ArcBufferPage are in scope.

public struct ArcBufferReaderInput(in ArcBuffer slice)
{
    private readonly ArcBuffer _slice = slice;
    private ArcBufferPage _page = slice.First;
    private int _position;

• Files reviewed: 6/6 changed files
• Comments generated: 5

[Copilot]

ArcBufferWriterWrapper is a new public type, but the committed API baseline in src/api/Orleans.Serialization/Orleans.Serialization.cs does not include it. Update the generated API surface file so this new public type is represented.

[Copilot]

Reader.Create(ArcBuffer, ...) is a new public API, but the committed API baseline file (src/api/Orleans.Serialization/Orleans.Serialization.cs) does not currently list this overload. Update the generated API surface file to include this new method.

[Copilot]

ArcBufferReaderInput is a new public type, but it is not present in the committed API baseline (src/api/Orleans.Serialization/Orleans.Serialization.cs). Update the generated API surface file so this type is captured for API review.

This issue also appears on line 121 of the same file.

Suggested change

	public struct ArcBufferReaderInput(in ArcBuffer slice)
	internal struct ArcBufferReaderInput(in ArcBuffer slice)

[Copilot]

This new public Deserialize<T>(ArcBuffer source) overload changes the Orleans.Serialization public API surface, but src/api/Orleans.Serialization/Orleans.Serialization.cs does not currently include it. Update the generated API surface file so the baseline matches the new API.

This issue also appears on line 883 of the same file.

[Copilot]

Writer.Create(ArcBufferWriter, ...) adds new public API surface in a packable src/ project, but src/api/Orleans.Serialization/Orleans.Serialization.cs does not currently include this overload. Update the generated API surface file to reflect the new API.