Refactor named-pipe serializers behind a shared typed base

[Copilot]

The IPC layer had the same BaseSerializer + INamedPipeSerializer boilerplate repeated across the platform and several extensions, with each serializer re-implementing the same Id / cast / Serialize / Deserialize shape. This change centralizes that pattern without changing the wire format or serializer registration model.

• Shared serializer abstraction

  • Added NamedPipeSerializer<T> in Microsoft.Testing.Platform as the common implementation of the INamedPipeSerializer plumbing.
  • Keeps the typed serialization contract in one place and leaves each concrete serializer responsible only for Id, DeserializeCore, and SerializeCore.

• Serializer migration

  • Moved the duplicated named-pipe serializers in Platform, MSBuild, HangDump, Retry, and TrxReport onto the new base.
  • Preserved existing message IDs and binary payload ordering; the change is structural, not protocol-level.

• Linked-source updates

  • Updated projects that embed the shared IPC serializer sources to include the new base file alongside BaseSerializer and VoidResponseSerializer.

• Focused test updates

  • Adjusted the IPC/protocol unit tests to exercise the refactored serializers while keeping the assertions on serialized behavior unchanged.

Example of the new shape:

internal sealed class ModuleInfoRequestSerializer
    : NamedPipeSerializer<ModuleInfoRequest>, INamedPipeSerializer
{
    public override int Id => 1;

    protected override ModuleInfoRequest DeserializeCore(Stream stream)
        => new(ReadString(stream), ReadString(stream), ReadString(stream));

    protected override void SerializeCore(ModuleInfoRequest value, Stream stream)
    {
        WriteString(stream, value.FrameworkDescription);
        WriteString(stream, value.ProcessArchitecture);
        WriteString(stream, value.TestResultFolder);
    }
}