Create the main execution loop for the virtual machine.

[yezzfusl]

1. In src/main.rs:

• Added a simple program to demonstrate the VM's functionality.
• Created instances of IOController and MemoryManagementUnit.
• Loaded the program into the CPU's memory and started execution.

2. In src/cpu.rs:

• Implemented the load_program method to load a program into memory.
• Created the main run method that executes the fetch-decode-execute cycle until the CPU is halted.
• Modified the decode_and_execute method to fetch operands for each instruction.
• Added a halted flag and a HALT instruction to stop execution.
• Implemented a print_registers method for debugging.
• Updated all instruction methods to take two operands.
• Added a comprehensive test that runs a small program in the VM.

[yezzfusl]

The main execution loop is effectively implemented, tying together the CPU emulator, memory management, and I/O operations.