Fixed-size struct without unsafe keyword, using "safe" S.R.CS.Unsafe

Test.cs

[StructLayout(LayoutKind.Sequential, Size = Size)]
public struct Test
{
    public const int Size = 32;
    public byte this[int idx] => Unsafe.AddByteOffset(ref Unsafe.As<Test, byte>(ref Unsafe.AsRef(in this)), (IntPtr)idx);

    public override string ToString()
    {
        Span<byte> bytes = stackalloc byte[Size];
        for (int i = 0; i < Size; i++)
        {
            var b = this[i];
            if (b == 0)
            {
                bytes = bytes.Slice(0, i);
                break;
            }

            bytes[i] = b;
        }
        // coule be UTF16, ASCII, etc
        // also see https://github.com/Spreads/Spreads/blob/master/src/Spreads.Core/DataTypes/Symbol.cs
        return Encoding.UTF8.GetString(bytes);
    }
}