Use virtual class for different cpu types rather than that hot mess with pointers and shiz

src/backend/core/BaseCPU.hpp

@@ -0,0 +1,12 @@
+#pragma once
+#include <Registers.hpp>
+
+namespace n64 {
+struct BaseCPU {
+  virtual ~BaseCPU() {}
+  virtual void Reset() {}
+  virtual int Run() {}
+  Registers regs;
+  Mem mem;
+};
+}