The address, adv payload and uuid fields of the event are pre-allocated by
modbluetooth, and reused in the IRQ handler. Simplify this and move all
storage into the `mp_obj_bluetooth_ble_t` instance.
This now allows users to hold on to a reference to these instances without
crashes, although they may be overwritten by future events. If they want
to hold onto the values longer term they need to copy them.
