UI: Add `MemoryInspector`

[AlessioC31]

Added a new UiTool to read values from memory.

I don't like very much how it is implemented but it was the only way (or at least the only one I found) to make it work since we have Gba<T: Cpu> and Cpu trait didn't have any method to access memory and memory is stored into an Rc<RefCell<>>.

Please tell me if you think it could be implemented in a better way (maybe without returning Ref? But I think it's needed since InternalMemory is managed by a RefCell).

It's very simple because I want to use it to debug an issue we may have in the instruction implementations. In the future, we could show a matrix with all the values and so on but for now I think this does the job.