Attempting to add NX bit

[DimaThenekov]

Thanks to the comment https://github.com/copy/v86/issues/845#issuecomment-2061179271 I tried adding the NX-bit, but I ran into the definition of read for execution and read for data. Can you give any implementation tips?

1. I understand that this is a difficult task, but the number of function calls to read from memory is too large. Can this be simplified?
2. Am I doing the right thing by storing the nx flag in tlb?
3. I also don't quite understand how the implementation of the nx bit can improve OS support, since this flag is only needed for security.
4. I don't know how to test this. I couldn't run any kvm tests other than realmode.flat.