Adapt tests that mutated Python event internals (`_event_id`, `_dict`,
direct attribute assignment, `FrozenEventV3(...)` construction) to work
with the new Rust-backed `Event` class:
- Rebuild events via `make_event_from_dict` / `make_test_event` instead
of patching attributes in place.
- Plumb `rejected_reason` through `_join_rules_event` rather than
assigning to `rejected_reason` after construction.
- Replace the hand-built event in `test_msc4242_state_dag` with a
`Mock(spec=EventBase)` since the test only needs a handful of
attributes.
- Add `# type: ignore` for the deprecated `event.user_id` / `event[key]`
accessors and for assigning to `event.content`.
- In `make_test_event`, drop the default `room_id` for v11+ create
events so each gets a distinct hash-derived room ID.
Erik Johnston
1cc69f1b76