Add underlying byte data for registers

- change backend logic for register r/w
- remade interface builder pattern for better syntactic sugar
- refined tests

MewTerminal/Program.cs

@@ -1,6 +1,7 @@
 using CommandLine;
 using CommandLine.Text;
 using MewTerminal.Commands;
+using MewTerminal.Commands.OnlineCommands;
 using MewtocolNet.Logging;
 using Spectre.Console;
 using System.Globalization;