Nice code

msgpack.cs

public static bool TryReadExtension(ReadOnlySpan<byte> buffer, out byte type, out IMemoryOwner<byte> extension, out int readSize)
{
    extension = null;
    return TryReadExtensionHeader(buffer, out type, out var length, out readSize)
        && length <= int.MaxValue
        && TryReadExtension(buffer, (int) length, ref extension, ref readSize);
}