Make AES256CBC independant of class variables.

[metalurgical]

The variables defined here are a code smell:

web3auth-unity-sdk/Assets/Plugins/Web3AuthSDK/Types/AES256CBC.cs

Lines 14 to 18 in 37b0d66

	private byte[] AES_ENCRYPTION_KEY;
	private byte[] ENCRYPTION_IV;
	private byte[] MAC_KEY;
	private byte[] ENCRYPTION_EPHEM_KEY;

They should rather be passed in as parameters to the relevant functions. This way an instance of this class is reusable for all encrypt and decrypt operations and no additional cognitive overhead is needed to keep track of which instance contains what.