v4.3.0

Release v4.3.0

Bugfix release for the subscription/notify feature added in v4.2.0.

- subscription destructor now also calls ubus_unregister_subscriber()
  (not only ubus_unsubscribe()); without it the subscriber object was
  left registered in the ubus context, so once the subscription state
  was freed the context held a dangling pointer -> use-after-free at the
  next object traversal / ubus_shutdown.
- ~ubus() clears the ubus_subscriber_cbs map too, matching the other
  static maps.
- Drop the unused subscription::state::cb (notify_trampoline reads the
  static map) and the dead iterator writes in uloop's common_task().
- uloop::exit() no longer re-memsets exit_task while it is still pending,
  so a second exit() in the same cycle can't corrupt a node that is
  still in the uloop tree.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: Oskari Rauta <oskari.rauta@gmail.com>