A nested state body cannot bind class attributes, so explicit id and transition-less Event are dropped

[fgmacedo]

NestedStateFactory.__new__ runs while the State.Compound / State.Parallel class body is
evaluated, which is before the owning statechart class exists. It has no cls, so it cannot do
the setattr that the top-level path does in StateMachineMetaclass.add_from_attributes.

Two documented differences follow from that, both introduced with the #643 fix in #645:

class ExplicitId(StateChart):
    class shire(State.Compound):
        bag_end = State(initial=True)
        green_dragon = State(final=True)

        visit_pub = Event(bag_end.to(green_dragon), id="pub.visit")

ExplicitId.events        # ['pub.visit'] -- registered
sm.send("pub.visit")     # works
ExplicitId.visit_pub     # AttributeError -- the top level would bind this

class Placeholder(StateChart):
    class shire(State.Compound):
        bag_end = State(initial=True)
        green_dragon = State(final=True)

        visit_pub = bag_end.to(green_dragon)
        knock = Event(name="Knock on the door")

Placeholder.knock        # AttributeError -- at the top level it is a class attribute

Both are pinned by tests in tests/test_statechart_compound.py
(test_explicit_id_wins_over_the_attribute_name, test_transition_less_event_declares_nothing).

The fix is #657: the nested body stops translating and stashes its raw
declarations on the State, and the metaclass reads them from add_state, where it has both
cls and the owning state.

When fixing: remove the note at the end of the Event section in docs/events.md and the
"two differences from the top-level form remain" paragraph in docs/releases/3.2.2.md, invert
the two tests above, and add an entry to the open release notes.