extmod/modbluetooth: Simplify management of pre-allocated event data.

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.

docs/library/ubluetooth.rst

@@ -52,6 +52,12 @@ Event Handling
     The optional *trigger* parameter allows you to set a mask of events that
     your program is interested in. The default is all events.
 
+    Note: the ``addr``, ``adv_data`` and ``uuid`` entries in the tuples are
+    references to data managed by the :mod:`ubluetooth` module (i.e. the same
+    instance will be re-used across multiple calls to the event handler). If
+    your program wants to use this data outside of the handler, then it must
+    copy them first, e.g. by using ``bytes(addr)`` or ``bluetooth.UUID(uuid)``.
+
     An event handler showing all possible events::
 
         def bt_irq(event, data):