Fix mem mgr not initialized

[dblnz]

Description

When running with tracing enabled, hyperlight returns mem_mgr not initialized error.

This is because to call the initialise API on a Hypervisor, and avoid the borrowing conflicts, we take mem_mgr from an option and put it back after the call finalizes.
However, when the guest exits for a IO/MMIO operation, the handle_io method checks for the mem_mgr before taking it, which will be None in this case and fail.

Fix

Avoid providing a reference to mem_mgr to the handle_mem_access function, and do that through the Hypervisor reference we already have in that place.
Caveat: The takeing and putting back of mem_mgr in handle_io still remains because handle_outb function takes mutable references to both mem_mgr and Hypervisor at the same time