Re-evaluate sandbox memory model #956

We should reconsider the requirements we have for the Hyperlight Sandbox and evaluate the sandbox memory model we have now, to decide whether it needs a complete redesign or small changes.

The main incentive for this discussion is the introduction of the mmaped memory, that at the moment, is treated separately, outside the Shared Memory that ensures exclusive access.

We would also benefit from a simplification of the model, if possible.