add memory hooks for cheat/rumble

[leiradel]

@RetroSven please report the correct amount of RAM to avoid the frontend trying to access memory outside the boundaries and crashing the core or overriding random memory and creating subtle bugs.

[RetroSven]

@leiradel It appears to me that everything ties back to "memory" which is defined here:

81/zx81/zx81.c:uint8_t memory[1024 * 1024];

So the size looks correct.

[leiradel]

I already said why this is wrong elsewhere.