Support padding in `Xor256`

[alexrp]

novadrop/src/formats/Cryptography/Xor256.cs

Lines 108 to 118 in 09d3a61

	public override PaddingMode Padding
	{
	get => base.Padding;
	set
	{
	// TODO: Support padding?
	_ = value == PaddingMode.None ? true : throw new CryptographicException();
	PaddingValue = value;
	}
	}

[alexrp]

https://github.com/dotnet/runtime/blob/eba3636d1484d951c1442abfceda868ea83bef21/src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/SymmetricPadding.cs